No Pairwise Interactions of GmSNAP18, GmSHMT08 and AtPR1 with Suppressed AtPR1 Expression Enhance the Susceptibility of Arabidopsis to Beet Cyst Nematode

GmSNAP18 and GmSHMT08 are two major genes conferring soybean cyst nematode (SCN) resistance in soybean. Overexpression of either of these two soybean genes would enhance the susceptibility of Arabidopsis to beet cyst nematode (BCN), while overexpression of either of their corresponding orthologs in Arabidopsis, AtSNAP2 and AtSHMT4, would suppress it. However, the mechanism by which these two pairs of orthologous genes boost or inhibit BCN susceptibility of Arabidopsis still remains elusive. In this study, Arabidopsis with simultaneously overexpressed GmSNAP18 and GmSHMT0 suppressed the growth of underground as well as above-ground parts of plants. Furthermore, Arabidopsis that simultaneously overexpressed GmSNAP18 and GmSHMT08 substantially stimulated BCN susceptibility and remarkably suppressed expression of AtPR1 in the salicylic acid signaling pathway. However, simultaneous overexpression of GmSNAP18 and GmSHMT08 did not impact the expression of AtJAR1 and AtHEL1 in the jasmonic acid and ethylene signaling pathways. GmSNAP18, GmSHMT08, and a pathogenesis-related (PR) protein, GmPR08-Bet VI, in soybean, and AtSNAP2, AtSHMT4, and AtPR1 in Arabidopsis could interact pair-wisely for mediating SCN and BCN resistance in soybean and Arabidopsis, respectively. Both AtSNAP2 and AtPR1 were localized on the plasma membrane, and AtSHMT4 was localized both on the plasma membrane and in the nucleus of cells. Nevertheless, after interactions, AtSNAP2 and AtPR1 could partially translocate into the cell nucleus. GmSNAP18 interacted with AtSHMT4, and GmSHMT4 interacted with AtSNAP2. However, neither GmSNAP18 nor GmSHMT08 interacted with AtPR1. Thus, no pairwise interactions among α-SNAPs, SHMTs, and AtPR1 occurred in Arabidopsis overexpressing either GmSNAP18 or GmSHMT08, or both of them. Transgenic Arabidopsis overexpressing either GmSNAP18 or GmSHMT08 substantially suppressed AtPR1 expression, while transgenic Arabidopsis overexpressing either AtSNAP2 or AtSHMT4 remarkably enhanced it. Taken together, no pairwise interactions of GmSNAP18, GmSHMT08, and AtPR1 with suppressed expression of AtPR1 enhanced BCN susceptibility in Arabidopsis. This study may provide a clue that nematode-resistant or -susceptible functions of plant genes likely depend on both hosts and nematode species.


Introduction
Plant parasitic nematodes (PPNs) are one of the most destructive pests in agriculture worldwide.PPNs with high virulence are widely spread in a broad range of commercially important crop families, such as Solanaceae, Fabaceae, Malvaceae, Amaranthaceae, and Poaceae.Furthermore, PPNs can survive in the soil for a long time before infesting again Plants 2023, 12, 4118 2 of 15 when suitable hosts emerge.Therefore, PPNs are difficult to control.As a result, they pose a large threat to the safety of global agricultural production [1].As the most damaging nematodes in the family Heteroderidae, cyst nematodes cause huge annual yield losses globally.For instance, soybean cyst nematode (SCN, Heterodera glycines), a destructive pathogen in soybean (Glycine max (L.) Merr.) production worldwide, causes more than USD 1.5 billion of yield losses annually in the United States alone [2][3][4].Currently, the most effective, economical, and environmentally friendly measure to control this pathogen is planting resistant soybean varieties.It is therefore important but challenging to map loci and clone the genes underlying SCN resistance for molecular breeding.
GmSNAP18 on rhg1 plays an important role in the cyst nematode resistance of soybeans.In resistant soybean varieties infected by SCN, GmSNAP18 would be abnormally accumulated in the feeding sites (syncytia), which showed cytotoxicity to cells, while the soybean NSF Ran07 could balance such cytotoxicity to maintain not only plant growth but also SCN resistance [15,16].Recently, two syntaxins (Glyma.12g194800and Glyma.16g154200) were reported to be able to target GmSNAP18 to mediate soybean SCN resistance [17].A new Qa-SNARE protein, GmSYP31A, could interact with GmSNAP18 to regulate mitochondrial membrane signaling, thereby inducing cell death at SCN feeding sites and modulating resistance against SCN [18].GmSHMT08 impacted one-carbon folate metabolism by mediating soybean SCN resistance [11,19].Rhg4 also showed tandem repeats of a genomic segment of about 35.7 kb, which contains three genes: Glyma.08g108800,GmSHMT08, and Glyma.08g109000[20].The pathogenesis-related protein GmPR08-Bet VI (Glyma.08g2320500)was involved in the resistance of soybean to SCN through interactions with both GmSNAP18 and GmSHMT08 [21].However, the resistance mechanisms of GmSNAP18 and GmSHMT08 are still poorly known.Butler et al. (2019) reported that overexpression of the rhg1-b carrying those three SCN-resistant genes in Arabidopsis and potato inhibited root and tuber growth, while enhancing resistance to beet cyst nematode (BCN, Heterodera schachtii) and potato cyst nematode (PCN, Globodera rostochiensis) [22].However, neither rhg1-a GmSNAP18 nor Rhg4 GmSHMT08 have been extended to other plant species for application in cyst nematode management.Our recent work studied whether rhg1-a GmSNAP18 and Rhg4 GmSHMT08, in addition to their orthologs in Arabidopsis, AtSNAP2 (an α-SNAP, At3g56190) and At-SHMT4 (At4g13930), also conferred resistance to BCN using transgenic Arabidopsis.The obtained results revealed the opposite BCN-infection phenotypes of Arabidopsis between overexpressing GmSNAP18 and AtSNAP2, and between overexpressing GmSHMT08 and AtSHMT4: overexpression of either GmSNAP18 or GmSHMT08 enhanced BCN susceptibility of Arabidopsis, while overexpression of either AtSNAP2 or AtSHMT4 could suppress the susceptibility of Arabidopsis to BCN [23].However, the resistance or susceptibility mechanisms of these α-SNAPs and SHMTs against BCN are unknown.In this study, we obtained the transgenic Arabidopsis simultaneously overexpressing rhg1-a GmSNAP18 and Rhg4 GmSHMT08, evaluated their BCN-infection phenotypes, and analyzed their susceptibility mechanism against BCN together with the previously reported data.

Simultaneous Overexpression of GmSNAP18 and GmSHMT08 Suppressed the Growth of Arabidopsis
Overexpression of rhg1-a GmSNAP18 (hereafter used as GmSNAP18) impacted neither plant height nor root length, while overexpression of GmSHMT08 stimulated plant height but did not affect root length in Arabidopsis [23].In this study, we harvested seeds of two homologous T2 generation transgenic Arabidopsis lines simultaneously overexpressing GmSNAP18 and GmSHMT08, OE-GmSNAP18/GmSHMT08-1 and OE-GmSNAP18/GmSHMT08-2 (Figure 1A), whose T3 generation plants were then used for the following measurements and analyses, including BCN-infection phenotyping.Concurrent overexpression of GmSNAP18 and GmSHMT08 substantially suppressed plant height when compared to wild-type Arabidopsis Col-0 (n ≥ 10) (Figure 1B,C).No significant difference in root length was shown between the transgenic Arabidopsis simultaneously overexpressing GmSNAP18 and GmSHMT08 and wild-type Arabidopsis Col-0 (Figure 1D).However, the fresh root weight of the transgenic Arabidopsis was remarkably decreased compared to wild-type Arabidopsis Col-0 (n ≥ 5) (Figure 1E).These results indicated that simultaneous overexpression of GmSNAP18 and GmSHMT08 suppressed the growth of both above-ground and under-ground parts of the transgenic Arabidopsis, different from individual overexpression of either GmSNAP18 or GmSHMT08 in Arabidopsis [23].

Simultaneous Overexpression of GmSNAP18 and GmSHMT08 Suppressed the Growth of Arabidopsis
Overexpression of rhg1-a GmSNAP18 (hereafter used as GmSNAP18) impacted neither plant height nor root length, while overexpression of GmSHMT08 stimulated plant height but did not affect root length in Arabidopsis [23].In this study, we harvested seeds of two homologous T2 generation transgenic Arabidopsis lines simultaneously overexpressing GmSNAP18 and GmSHMT08, OE-GmSNAP18/GmSHMT08-1 and OE-GmSNAP18/GmSHMT08-2 (Figure 1A), whose T3 generation plants were then used for the following measurements and analyses, including BCN-infection phenotyping.Concurrent overexpression of GmSNAP18 and GmSHMT08 substantially suppressed plant height when compared to wild-type Arabidopsis Col-0 (n ≥ 10) (Figure 1B, C).No significant difference in root length was shown between the transgenic Arabidopsis simultaneously overexpressing GmSNAP18 and GmSHMT08 and wild-type Arabidopsis Col-0 (Figure 1D).However, the fresh root weight of the transgenic Arabidopsis was remarkably decreased compared to wild-type Arabidopsis Col-0 (n ≥ 5) (Figure 1E).These results indicated that simultaneous overexpression of GmSNAP18 and GmSHMT08 suppressed the growth of both above-ground and under-ground parts of the transgenic Arabidopsis, different from individual overexpression of either GmSNAP18 or GmSHMT08 in Arabidopsis [23].

Simultaneous Overexpression of GmSNAP18 and GmSHMT08 Enhanced Susceptibility of Arabidopsis to BCN
Subsequently, the BCN-infection phenotypes of transgenic Arabidopsis simultaneously overexpressing GmSNAP18 and GmSHMT08 were evaluated.Clearly, at 20 days postinoculation (dpi) of BCN, the numbers of females per plant simultaneously overexpressing GmSNAP18 and GmSHMT08 were substantially increased when compared to wild-type Arabidopsis Col-0 (n ≥ 9) (Figure 2A).At 35 dpi, compared to wild-type Arabidopsis Col-0, the total numbers of both females and cysts per plant simultaneously overexpressing GmSNAP18 and GmSHMT08 were also significantly elevated (n ≥ 12) (Figure 2B-D).As stated above, simultaneous overexpression of GmSNAP18 and GmSHMT08 inhibited the root growth of Arabidopsis (Figure 1D,E), so the BCN-infection phenotype of the transgenic Arabidopsis is unrelated to root growth status.It could therefore be concluded from these obtained results that simultaneous overexpression of GmSNAP18 and GmSHMT08 boosted the susceptibility of Arabidopsis to BCN.

Simultaneous Overexpression of GmSNAP18 and GmSHMT08 Suppressed the Expression Patterns of AtPR1 on the Salicylic Acid Signaling Pathway in Arabidopsis
Arabidopsis AtPR1 (At2g14610) rather than AtPR5 (At1g75040) interacted with At-SNAP2, AtSHMT4, and the BCN effector HsSNARE1, which was involved in mediating BCN susceptibility [24].In this work, the expression patterns of both AtPR1 and AtPR5 on the salicylic acid (SA) signaling pathway in the transgenic Arabidopsis simultaneously overexpressing GmSNAP18 and GmSHMT08 were analyzed.The results clearly indicated that overexpression of both GmSNAP18 and GmSHMT08 substantially suppressed expression of AtPR1; in contrast, overexpression of both GmSNAP18 and GmSHMT08 did not remarkably impact expression of AtPR5, in the transgenic Arabidopsis when compared to wild-type Arabidopsis Col-0, after infected by BCN, no matter at 36 h post-inoculation (hpi) or 5 dpi (Figure 3A,B).

Simultaneous Overexpression of GmSNAP18 and GmSHMT08 Did Not Impact Expression Patterns of AtJAR1 and AtHEL1 on the Jasmonic Acid and Ethylene Signaling Pathways in Arabidopsis
Subsequently, we studied whether simultaneous overexpression of GmSNAP18 and GmSHMT08 impacted the expression patterns of AtJAR1 (At2g46370) and AtHEL1 (At3g04720) on the jasmonic acid (JA) and ethylene (ET) signaling pathways in Arabidopsis.The results showed that, compared to wild-type Arabidopsis Col-0, expression patterns of neither AtJAR1 nor AtHEL1 showed similar trends in both transgenic lines at 5 dpi (Figure 3C,D).Thus, expression patterns of AtJAR1 and AtHEL1 were not associated with GmSNAP18 and GmSHMT08 expression in Arabidopsis, meaning simultaneous overexpression of GmSNAP18 and GmSHMT08 might not impact the JA and ET signaling pathways.and in the nucleus, while AtPR1 and AtSHMT4 could interact only in the nucleus of Nicotiana benthamiana cells (Figure 5), suggesting the translocation of AtSNAP2 and AtPR1 into the nucleus of cells after interactions due to AtSHMT4.overexpressing GmSNAP18 and GmSHMT08 were analyzed.The results clearly indicated that overexpression of both GmSNAP18 and GmSHMT08 substantially suppressed expression of AtPR1; in contrast, overexpression of both GmSNAP18 and GmSHMT08 did not remarkably impact expression of AtPR5, in the transgenic Arabidopsis when compared to wild-type Arabidopsis Col-0, after infected by BCN, no matter at 36 h post-inoculation (hpi) or 5 dpi (Figure 3A,B).

Simultaneous Overexpression of GmSNAP18 and GmSHMT08 Did Not Impact Expression Patterns of AtJAR1 and AtHEL1 on the Jasmonic Acid and Ethylene Signaling Pathways in Arabidopsis
Subsequently, we studied whether simultaneous overexpression of GmSNAP18 and GmSHMT08 impacted the expression patterns of AtJAR1 (At2g46370) and AtHEL1 (At3g04720) on the jasmonic acid (JA) and ethylene (ET) signaling pathways in Arabidop- The relative expression levels were obtained after comparing them to those in the wild-type plants at 0 hpi, which was set as '1 ′ .The experiments were repeated three times, with a similar trend.The significant difference was statistically analyzed by the one-way ANOVA method using the software Graphpad 8.0.ns: No significance; *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Subcellular and Interaction Localizations of AtSNAP2, AtSHMT4, and AtPR1
The subcellular localization analyses showed that both AtSNAP2 and AtPR1 were localized on the plasma membrane of cells, while AtSHMT4 was localized in the cell nucleus besides on the plasma membrane of cells of Nicotiana benthamiana (Figure 4A,B).AtSNAP2, AtSHMT4, and AtPR1 could interact pair-wisely [24].We further analyzed the localization of their interactions.The BiFC assays indicated that interactions between AtSNAP2 and AtSHMT4, and between AtPR1 and AtSNAP2 could occur both on the plasma membrane and in the nucleus, while AtPR1 and AtSHMT4 could interact only in the nucleus of Nicotiana benthamiana cells (Figure 5), suggesting the translocation of AtSNAP2 and AtPR1 into the nucleus of cells after interactions due to AtSHMT4.
AtSHMT4, and AtPR1 could interact pair-wisely [24].We further analyzed the localizatio of their interactions.The BiFC assays indicated that interactions between AtSNAP2 an AtSHMT4, and between AtPR1 and AtSNAP2 could occur both on the plasma membran and in the nucleus, while AtPR1 and AtSHMT4 could interact only in the nucleus of Nic tiana benthamiana cells (Figure 5), suggesting the translocation of AtSNAP2 and AtPR1 int the nucleus of cells after interactions due to AtSHMT4.

Discussion
Rhg4 and rhg1 (rhg1-a and rhg1-b) are two major QTL underlying SCN resistance in soybean [10,25].Both rhg1-a and Rhg4 are required for the SCN resistance of Peking-type soybeans, while rhg1-b is solely needed for the SCN resistance of PI 88788-type soybeans [5,10,25].GmSNAP18 and GmSHMT08 are the resistant genes on rhg1-a and Rhg4, respectively [11,12].In conjunction with our previous study [23], this present work studied the possibility of extension application of SCN-resistant rhg1-a GmSNAP18 and Rhg4 GmSHMT08 for management of cyst nematodes by simultaneously expressing them into Arabidopsis infected by BCN.However, overexpression of both rhg1-a GmSNAP18 and

Discussion
Rhg4 and rhg1 (rhg1-a and rhg1-b) are two major QTL underlying SCN resistance in soybean [10,25].Both rhg1-a and Rhg4 are required for the SCN resistance of Pekingtype soybeans, while rhg1-b is solely needed for the SCN resistance of PI 88788-type soybeans [5,10,25].GmSNAP18 and GmSHMT08 are the resistant genes on rhg1-a and Rhg4, respectively [11,12].In conjunction with our previous study [23], this present work studied the possibility of extension application of SCN-resistant rhg1-a GmSNAP18 and Rhg4 GmSHMT08 for management of cyst nematodes by simultaneously expressing them into Arabidopsis infected by BCN.However, overexpression of both rhg1-a GmSNAP18 and Rhg4 GmSHMT08 (Figure 2) or either of them [23] enhanced BCN susceptibility of Arabidopsis.These indicate different mechanisms of resistance and susceptibility of rhg1-a GmSNAP18 and Rhg4 GmSHMT08 to SCN and BCN in soybean and Arabidopsis, respectively.In contrast, overexpression of either AtSNAP2 or AtSHMT4, which are the orthologs of rhg1-a GmSNAP18 and Rhg4 GmSHMT4 in Arabidopsis, respectively, suppressed BCN susceptibility [23].
GmSNAP18, GmSHMT08, and GmPR08-Bet VI in soybean, and AtSNAP2, AtSHMT4, and AtPR1 in Arabidopsis could interact pair-wisely [21,24].A simple hypothesized molecular model of action for wild-type Arabidopsis Col-0 is shown in Figure 6A.GmSNAP18 interacted with AtSHMT4, and GmSHMT4 interacted with AtSNAP2; however, neither GmSNAP18 nor GmSHMT08 interacted with AtPR1 [23].Thus, no pairwise interactions among GmSNAP18, GmSHMT08, and AtPR1 occurred in Arabidopsis overexpressing either GmSNAP18 or GmSHMT08, or both of them.When compared to wild-type Arabidopsis Col-0, the transgenic Arabidopsis overexpressing both GmSNAP18 and GmSHMT08 substantially suppressed AtPR1 expression (Figure 3A), similar to the transgenic Arabidopsis overexpressing either GmSNAP18 or GmSHMT08 [23].Additionally, overexpression of either AtSNAP2 or AtSHMT4 substantially suppressed BCN susceptibility and remarkably enhanced AtPR1 expression in the transgenic Arabidopsis compared to wild-type Arabidopsis Col-0 [23].We thus hypothesized the simple models of action for different types of α-SNAPs, SHMTs, and AtPR1 in the mediation of BCN susceptibility in Arabidopsis (Figure 6B-F).Taken together, no pairwise interactions of GmSNAP18, GmSHMT08, and AtPR1 with suppressed AtPR1 expression enhanced BCN susceptibility in Arabidopsis.
Expression of AtPR1 on the SA signaling pathway would be suppressed in transgenic Arabidopsis overexpressing both rhg1-a GmSNAP18 and Rhg4 GmSHMT08 or either of them; in contrast, AtPR1 expression would be stimulated in transgenic Arabidopsis overexpressing either AtSNAP2 or AtSHMT4 (Figure 4; ref. [23]).However, the expression pattern of AtPR5 was not impacted by the simultaneous overexpression of GmSNAP18 and GmSHMT08 in Arabidopsis after infection with BCN (Figure 3B).Furthermore, the expression pattern of neither AtJAR1 nor AtHEL1 on the JA and ET signaling pathways was influenced by the simultaneous overexpression of GmSNAP18 and GmSHMT08 in Arabidopsis after infection with BCN (Figure 3C,D).In addition, cytokinins were reported to be involved in plant-pathogen interactions [26], but to the best of our knowledge, there are rarely reports about cytokinins in the mediation of soybean cyst nematode resistance.So, in this study, we did not measure the expression patterns of cytokinins in the transgenic Arabidopsis simultaneously overexpressing GmSNAP18 and GmSHMT08.These suggest BCN susceptibility of Arabidopsis may be mainly associated with the SA signaling pathway.Translocations of AtSNAP2 and AtPR1, both of which were localized on the plasma membrane, into the nucleus occurred in Nicotiana benthamiana cells after interactions due to AtSHMT4, which was localized both on the plasma membrane and in the nucleus of cells (Figures 4 and 5).Therefore, AtPR1 expression is mediated by the interactions of AtPR1 with AtSNAP2 and AtSHMT4 and the interaction between AtSNAP2 and AtSHMT4; while such pair-wise interactions are broken down, AtPR1 expression will be suppressed, as shown in the case of simultaneous overexpression of GmSNAP18 and GmSHMT08 in Arabidopsis (Figure 3A).Pathogenesis-related (PR) genes are one key component in the SA signaling pathway, which play an important role in plant-pathogen interactions and are particularly essential for regulating the resistance of plants to pathogens, including nematodes.Tomato PR-1 was a hallmark of the cultivar resistance against PCN conferred by the resistant gene Hero A [27].Tomato pathogenesis-related genes, particularly PR-1, were markedly involved in Mi-1-mediated and SA-induced resistance to root-knot nematodes (Meloidogyne incognita) [28].The resistance to SCN in soybean would be enhanced by overexpressing AtPR5 in susceptible soybean Williams 82 [29].In addition, GmPR08-Bet VI could interact with both Rhg4 GmSHMT08 and rhg1-a GmSNAP18 to be involved in mediating SCN resistance in Peking-type soybeans [21,30].Recently, our study revealed a novel mechanism for mediating BCN resistance of Arabidopsis via AtPR1: a BCN effector HsSNARE1 could interact with AtPR1 and AtSNAP2 via its N-terminal and t-SNARE domain, respectively, to Plants 2023, 12, 4118 10 of 15 form a super-complex composed of HsSNARE1, AtPR1, AtSNAP2, and AtSHMT4, which suppressed the expression of AtPR1 and ultimately promoted nematode parasitism [24].These combined comparisons further support that no pairwise interactions of GmSNAP18, GmSHMT08, and AtPR1 with suppressed expression of AtPR1 enhanced the susceptibility of Arabidopsis to BCN.Nuaima et al. (2023) studied six Heterodera schachtii populations that coincided with differences in invasion and propagation in plant roots, which show that the plant-nematode interaction between cruciferous plants and H. schachtii occurred in a hostand population-specific manner [31].The specialized interaction with each plant variety may explain why GmSNAP18 and GmSHMT08 show different interactions in soybean and Arabidopsis with SCN and BCN.
Plants 2023, 12, x FOR PEER REVIEW 10 of 15 study revealed a novel mechanism for mediating BCN resistance of Arabidopsis via AtPR1: a BCN effector HsSNARE1 could interact with AtPR1 and AtSNAP2 via its N-terminal and t-SNARE domain, respectively, to form a super-complex composed of HsSNARE1, AtPR1, AtSNAP2, and AtSHMT4, which suppressed the expression of AtPR1 and ultimately promoted nematode parasitism [24].These combined comparisons further support that no pairwise interactions of GmSNAP18, GmSHMT08, and AtPR1 with suppressed expression of AtPR1 enhanced the susceptibility of Arabidopsis to BCN.Nuaima et al. ( 2023) studied six Heterodera schachtii populations that coincided with differences in invasion and propagation in plant roots, which show that the plant-nematode interaction between cruciferous plants and H. schachtii occurred in a host-and population-specific manner [31].The specialized interaction with each plant variety may explain why GmSNAP18 and GmSHMT08 show different interactions in soybean and Arabidopsis with SCN and BCN.However, overexpression of soybean rhg1-b carrying 3 resistant genes (rhg1-b Gm-SNAP18, GmAAT, and GmWI12; ref. [6]) suppressed BCN susceptibility in Arabidopsis [22], in contrast to simultaneous overexpression of rhg1-a GmSNAP18 and Rhg4 GmSHMT08 in Arabidopsis (Figure 2).Cyst nematode resistance of rhg1-b in both soybean and Arabidopsis may not require involvement of the PRs on the SA signaling pathway; in contrast, cyst nematode resistance and susceptibility of rhg1-a GmSNAP18 and Rhg4 GmSHMT08 in soybean and Arabidopsis, respectively, are essentially associated with the PRs-related SA signaling pathway, which is worthy of further study.As we know, rational control of the nematodes is critical to helping improve crop yields globally.As a result, exploiting plant resistance and the molecular mechanisms underlying plant-nematode interactions is key when materializing the impacts on a case-by-case basis [32].This will help us optimize PPN control by combining them with other tactics in integrated management.

Plant Materials and Nematodes
Arabidopsis Col-0 was used as the wild-type.Arabidopsis plants were grown under long-day conditions (16 h light/8 h dark cycles) at 24 • C. Nicotiana benthamiana was planted in soil and grew under a 16 h light/8 h dark photoperiod at 24-25 • C. BCN was used as the nematode and propagated on beets (Beta vulgaris L.) [23].

Gene Cloning and Plasmid Construction
For the construction of transgenic Arabidopsis, cDNAs of rhg1-a GmSNAP18 and GmSHMT08 were, respectively, cloned into pH7WG2D and pDT7 with a CaMV35S promoter (pCaMV35S) to generate pH7WG2D: rhg1-a GmSNAP18 and pDT7:GmSHMT08 using a ClonExpress II One Step Cloning kit (Vazyme, Nanjing, China).cDNAs of rhg1-a GmSNAP18 and GmSHMT08 were cloned from the soybean cultivar (cv.)Forrest, which shows Peking-type SCN resistance, using PrimeSTAR ® Max DNA Polymerase (Takara, Kusatsu, Japan).Total RNA was extracted with a TRIzol TM Reagent (Invitrogen, Vilnius, Lithuania), and the cDNA was synthesized using a HiScript III 1st Strand cDNA Synthesis Kit (+gDNA wiper) (Vazyme, Nanjing, China).

Arabidopsis Transformation and Molecular Identification
The two constructs pH7WG2D:rhg1-a GmSNAP18 and pDT7:GmSHMT08 were first, respectively, transformed into Agrobacterium tumefaciens GV3101 using the freeze-thaw method.Subsequently, Arabidopsis transformation was conducted by the flower bud soaking method [33].The transformed seedlings were drained a little and grew for 24 h in the dark and then under the normal growth conditions of long-day conditions (16 h light/8 h dark cycles) at 24 °C.The harvested T1 seeds were screened on the 1/2 MS medium with BASTA and hygromycin to obtain positive seedlings, which were further identified by RT-PCR using the corresponding primers listed in Table 1, generating a rhg1-a GmSNAP18 fragment of 119 bp, and a GmSHMT08 fragment of 252 bp.AtActin (At5g09810) was used as the reference gene.The positive seedlings were transferred into soils to grow and harvest T2 seeds for each plant as the transgene lines (OE-GmSNAP18/GmSHMT08).The homologous T3 generation plants were used for analyses including growth status, BCN-infection phenotyping, gene expression patterns.

Growth Parameter Measurement of Transgenic Arabidopsis
At least 20 seedlings each transgenic Arabidopsis line (OE-GmSNAP18/GmSHMT08-1 and OE-GmSNAP18/GmSHMT08-2) were planted in the soil for measurement of growth

Figure 3 .
Figure 3. Expression patterns of AtPR1, AtPR5, AtJAR1, and AtHEL1 in GmSNAP18 and GmSHMT08simultaneously overexpressed Arabidopsis infected by BCN.(A) Expression patterns of AtPR1.(B) Expression patterns of AtPR5.(C) Expression patterns of AtJAR1.(D) Expression patterns of AtHEL1.The relative expression levels were obtained after comparing them to those in the wild-type plants at 0 hpi, which was set as '1'.The experiments were repeated three times, with a similar trend.The significant difference was statistically analyzed by the one-way ANOVA method using the software Graphpad 8.0.ns: No significance; *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Figure 3 .
Figure 3. Expression patterns of AtPR1, AtPR5, AtJAR1, and AtHEL1 in GmSNAP18 and GmSHMT08simultaneously overexpressed Arabidopsis infected by BCN.(A) Expression patterns of AtPR1.(B) Expression patterns of AtPR5.(C) Expression patterns of AtJAR1.(D) Expression patterns of AtHEL1.The relative expression levels were obtained after comparing them to those in the wild-type plants at 0 hpi, which was set as '1 ′ .The experiments were repeated three times, with a similar trend.The significant difference was statistically analyzed by the one-way ANOVA method using the software Graphpad 8.0.ns: No significance; *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Figure 6 .
Figure 6.Hypothesized molecular models of action for mediation of BCN susceptibility of Arabidopsis.(A-F) Hypothesized molecular models of action for mediation of BCN susceptibility of wild-type Arabidopsis Col-0 and transgenic Arabidopsis overexpressing both GmSNAP18 and GmSHMT08 or either of them, or either of AtSNAP2 or AtSHMT4.The models denote that AtSNAP2,

Figure 6 .
Figure 6.Hypothesized molecular models of action for mediation of BCN susceptibility of Arabidopsis.(A-F) Hypothesized molecular models of action for mediation of BCN susceptibility of wild-type Arabidopsis Col-0 and transgenic Arabidopsis overexpressing both GmSNAP18 and GmSHMT08 or either of them, or either of AtSNAP2 or AtSHMT4.The models denote that AtSNAP2, AtSHMT4, and AtPR1 interacted pair-wisely in (A,E,F), but GmSNAP18/AtSNAP2, GmSHMT08/AtSHMT4, and AtPR1 did not interact pair-wisely in (B-D).OE: Overexpression.

Table 1 .
List of the primers used in this study.