The SlSWEET12c Sugar Transporter Promotes Sucrose Unloading and Metabolism in Ripening Tomato Fruits
Round 1
Reviewer 1 Report
The authors comprehensively characterized the sugar transporter gene SlSWEET12c in the tomato S. lycopersicum. The gene expression and its tissue and intracellular localization were analyzed. Transgenic plants with gene silencing and overexpression have also been obtained and characterized. The manuscript can be accepted for publication in the Horticulturae after minor but serious revision.
First of all, there is a problem with the availability and identification of data in the article.
Namely, the names of proteins of the tomato SWEET family do not correlate in any way with the NCBI data. For example, a search in NCBI for the SlSWEET1a gene returns ‘LOC101244279 bidirectional sugar transporter SWEET1-like [Solanum lycopersicum (tomato)]’. At the same time, BLAST analysis of the primers used by the authors for this gene (Table S1) leads to a completely different tomato gene – ‘LOC101258946 bidirectional sugar transporter SWEET1-like [Solanum lycopersicum (tomato)]’.
Moreover, the subject of this study, the gene named SlSWEET12c, does not exist in publicly available databases (NCBI or SolGenomics). An intriguing quest to find out what it could be, using the number Solyc05g024260 (Line 127 of the manuscript), found the "RAG1-activating protein 1 homolog" gene, which, according to the article [https://doi.org/10.1038/nature09606], belongs to the SWEET1 subfamily. BLAST search using primers (Table S1) revealed the gene "LOC101255592 bidirectional sugar transporter N3 [Solanum lycopersicum (tomato)]". A further search for the name SlSWEET12 in NCBI yielded as many as 2 genes: "LOC101265550 bidirectional sugar transporter SWEET12 [Solanum lycopersicum (tomato)]" and "LOC112940022 bidirectional sugar transporter SWEET12-like [Solanum lycopersicum (tomato)]".
Actually, a note: the authors should give in their work access numbers of genes either according to NCBI or according to the SolGenomics database, not only for SlSWEET12c, but also for all other genes used for analysis of expression. This can be done by adding a column with access numbers to Table S1.
Other comments:
Lines 99, 211: ‘…the tomato database website…’
Here the authors should give the address of the website of the database.
Figure 1: ‘(a) Relative expression levels of SlSWEET genes analyzed with RT-qPCR.’
In the caption to the Figure 1, in paragraph (a), it should be clarified in which tissues the expression was measured.
Line 377: ‘Phylogenetic analysis indicated that SlSWEET12c belonged to clade III.’
Neither in the Results, nor in the Materials-Methods is there any information about the phylogenetic analysis of tomato SWEET genes. It would be nice to provide (at least in additional files) a dendrogram built on the basis of protein sequences of tomato SWEETs and, for example, model plants Arabidopsis and rice SWEETs (especially, if AtSWEETs and OsSWEETs are used for comparison in discussion – lines 380-383, 450).
The design of the OE-SlSWEET12c vector looks interesting (Fig. S4). It appears that the SlSWEET12c gene does not have a promoter. The 35S promoter is drawn on both sides of the gene: one (on the right), judging by the direction of the arrow, triggers the expression of the GUS gene; the other (on the left) has unknown target. The scheme needs to be revised.
Author Response
Reviewer 1:
The authors comprehensively characterized the sugar transporter gene SlSWEET12c in the tomato S. lycopersicum.......
First of all, there is a problem with the availability and identification of data in the article.
Namely, the names of proteins of the tomato SWEET family do not correlate in any way with the NCBI data......
Response: The tomato SWEET family has been reported by Feng et al in 2015. (“Genome-wide identification, phylogeny, and expression analysis of the SWEET gene family in tomato”). In this study, the NCBI data of tomato SWEET family members has been shown. When searching SlSWEET12c in the NCBI, we can get two articles also use the name with SlSWEET12c[1,2]. For the primers shown in Table S1, it is refer to Ho et al(2019)[3].
- Ru L, He Y, Zhu Z, Patrick JW, Ruan YL. Integrating sugar metabolism with transport: elevation of endogenous cell wall invertase activity up-regulates SlHT2 and SlSWEET12cexpression for early fruit development in tomato. Front Genet. 2020, 11:592596. doi: 10.3389/fgene.2020.592596.
- Sun L, Wang J, Lian L, Song J, Du X, Liu W, Zhao W, Yang L, Li C, Qin Y, Yang R. Systematic analysis of the sugar accumulation mechanism in sucrose- and hexose- accumulating cherry tomato fruits. BMC Plant Biol. 2022, 22(1):303. doi: 10.1186/s12870-022-03685-8.
- Ho LH, Klemens PAW, Neuhaus HE, Ko HY, Hsieh SY, Guo WJ. SlSWEET1a is involved in glucose import to young leaves in tomato plants. J Exp Bot. 2019 Jun 28;70(12):3241-3254. doi: 10.1093/jxb/erz154.
Other comments:
- Lines 99, 211: ‘…the tomato database website…’
Here the authors should give the address of the website of the database.
Response: Thanks for reviewing, the website has added in lines 99 and 211.
- Figure 1: ‘(a) Relative expression levels of SlSWEET genes analyzed with RT-qPCR.’In the caption to the Figure 1, in paragraph (a), it should be clarified in which tissues the expression was measured.
Response:We have revised as “(a) Relative expression levels of SlSWEET genes analyzed with RT-qPCR. The cDNA is isolated from fruits in RR stage.”
- Line 377: ‘Phylogenetic analysis indicated that SlSWEET12c belonged to clade III.’
Neither in the Results, nor in the Materials-Methods is there any information about the phylogenetic analysis of tomato SWEET genes. It would be nice to provide (at least in additional files) a dendrogram built on the basis of protein sequences of tomato SWEETs and, for example, model plants Arabidopsis and rice SWEETs (especially, if AtSWEETs and OsSWEETs are used for comparison in discussion – lines 380-383, 450).
Response: The phylogenetic analysis of tomato SWEET genes has already done in the previous study, the reference has added in line 385.
-
The design of the OE-SlSWEET12c vector looks interesting (Fig. S4). It appears that the SlSWEET12c gene does not have a promoter. The 35S promoter is drawn on both sides of the gene: one (on the right), judging by the direction of the arrow, triggers the expression of the GUS gene; the other (on the left) has unknown target. The scheme needs to be revised
Response: Thanks for your reviewing, the OE-SlSWEET12c vector has corrected in supplementary S4. Also the restriction restriction sites have changed in line 153.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Congratulations on your research and article !
Comments for author File: 
Comments.pdf
Author Response
Reviewer 2:
Congratulations on your research and article !
Response: Thanks for your congratulations. We are so glad to the review you have given. It’s our great honor.
Author Response File: Author Response.docx
