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35 pages, 3909 KiB

Open AccessReview

Pollen–Pistil Interaction During Distant Hybridization in Plants

by Ekaterina V. Zakharova, Alexej I. Ulianov, Yaroslav Yu. Golivanov, Tatiana P. Molchanova, Yuliya V. Orlova and Oksana A. Muratova

Agronomy 2025, 15(7), 1732; https://doi.org/10.3390/agronomy15071732 - 18 Jul 2025

Viewed by 872

Abstract

A combination of high potential productivity and ecological stability is essential for current cultivars, which is achievable by breeding. Interspecific/intergeneric hybridization remains a key approach to producing new high-yielding and resistant cultivars. Interspecific reproductive barriers (IRBs) appear in the interaction between the pollen and pistil of interspecific/intergeneric hybrids. The mechanisms underlying these hybridization barriers are to a considerable degree unknown. The pollen–pistil interaction is decisive because the pollen of distantly related plant species either is not recognized by stigma cells or is recognized as foreign, preventing pollen tube (PT) germination and/or penetration into the stigma/style/ovary. This review mainly focuses on (1) the pollen–pistil system; (2) IRB classification; (3) similarity and differences in the function of self-incompatibility (SI) barriers and IRBs; and (4) physiological and biochemical control of IRBs and their overcoming. The main goal is to illuminate the physiological, biochemical, and molecular mechanisms underlying the growth arrest of incompatible PTs and their death. In general, this review consolidates the current understanding of the interaction of the male gametophyte with the sporophyte tissues of the pistil and outlines future research directions in the area of plant reproductive biology. Full article

(This article belongs to the Section Plant-Crop Biology and Biochemistry)

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21 pages, 10197 KiB

Open AccessArticle

Pre- and Post-Zygotic Barriers Contribute to Reproductive Isolation and Correlate with Genetic Distance in Cucumis

by María Ferriol, Unzué Simó, Carme J. Mansanet, Alejandro Torres, Belén Picó, Antonio J. Monforte and Carlos Romero

Plants 2023, 12(4), 926; https://doi.org/10.3390/plants12040926 - 17 Feb 2023

Cited by 7 | Viewed by 3636

Abstract

Hybridization between Cucumis species, including cultivated melon (C. melo), is hampered by Interspecific Reproductive Barriers (IRBs). However, the nature of IRBs in Cucumis is largely unknown. This study explores locations, timing, and contribution to reproductive isolation (RI) of pre- and post-zygotic IRBs in Cucumis. To do this, we assessed crossability among Cucumis African wild species and C. melo at the pre-zygotic level by visualizing pollen tubes under fluorescence microscopy and, post-zygotically, by evaluating fruit/seed set and F₁ hybrid fertility. Genetic distances among Cucumis species were inferred from Genotyping-by-Sequencing, and its correlation with RI stages was analyzed. Observed pre- and post-zygotic IRBs included pollen tube arrest, fruit set failure, and hybrid male sterility. Unilateral cross-incongruity/incompatibility (UCI) was detected in some hybridizations, and dominant gene action is suggested for pistil-side UCI in interspecific F₁ hybrids. Notably, the allotetraploid C. ficifolius was very fertile as a seed parent but infertile in all reciprocal crosses. Contribution to RI was found significant for both pre- and post-zygotic IRBs. Additionally, a significant positive correlation was detected between genetic distance and pre- and post-zygotic RI stages. Interestingly, UCI offers an accessible system to dissect the genetics of IRBs in Cucumis, which may facilitate the use of wild relatives in breeding. Full article

(This article belongs to the Section Plant Genetic Resources)

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15 pages, 2093 KiB

Open AccessArticle

A Cysteine-Rich Protein, SpDIR1L, Implicated in S-RNase-Independent Pollen Rejection in the Tomato (Solanum Section Lycopersicon) Clade

by Juan Vicente Muñoz-Sanz, Alejandro Tovar-Méndez, Lu Lu, Ru Dai and Bruce McClure

Int. J. Mol. Sci. 2021, 22(23), 13067; https://doi.org/10.3390/ijms222313067 - 2 Dec 2021

Cited by 11 | Viewed by 2869

Abstract

Tomato clade species (Solanum sect. Lycopersicon) display multiple interspecific reproductive barriers (IRBs). Some IRBs conform to the SI x SC rule, which describes unilateral incompatibility (UI) where pollen from SC species is rejected on SI species’ pistils, but reciprocal pollinations are successful. However, SC x SC UI also exists, offering opportunities to identify factors that contribute to S-RNase-independent IRBs. For instance, SC Solanum pennellii LA0716 pistils only permit SC Solanum lycopersicum pollen tubes to penetrate to the top third of the pistil, while S. pennellii pollen penetrates to S. lycopersicum ovaries. We identified candidate S. pennellii LA0716 pistil barrier genes based on expression profiles and published results. CRISPR/Cas9 mutants were created in eight candidate genes, and mutants were assessed for changes in S. lycopersicum pollen tube growth. Mutants in a gene designated Defective in Induced Resistance 1-like (SpDIR1L), which encodes a small cysteine-rich protein, permitted S. lycopersicum pollen tubes to grow to the bottom third of the style. We show that SpDIR1L protein accumulation correlates with IRB strength and that species with weak or no IRBs toward S. lycopersicum pollen share a 150 bp deletion in the upstream region of SpDIR1L. These results suggest that SpDIR1L contributes to an S-RNase-independent IRB. Full article

(This article belongs to the Special Issue Pollen-Pistil Interaction)

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25 pages, 3526 KiB

Open AccessArticle

HD-AGPs as Speciation Genes: Positive Selection on a Proline-Rich Domain in Non-Hybridizing Species of Petunia, Solanum, and Nicotiana

by Tara D. Callaway and Anu Singh-Cundy

Plants 2019, 8(7), 211; https://doi.org/10.3390/plants8070211 - 8 Jul 2019

Cited by 9 | Viewed by 5117

Abstract

Transmitting tissue-specific proteins (TTS proteins) are abundant in the extracellular matrix of Nicotiana pistils, and vital for optimal pollen tube growth and seed set. We have identified orthologs from several species in the Solanaceae, including Petunia axillaris axillaris and Petunia integrifolia. We refer to TTS proteins and their orthologs as histidine domain-arabinogalactan proteins (HD-AGPs). HD-AGPs have distinctive domains, including a small histidine-rich region and a C-terminal PAC domain. Pairwise comparisons between HD-AGPs of 15 species belonging to Petunia, Nicotiana, and Solanum show that the his-domain and PAC domain are under purifying selection. In contrast, a proline-rich domain (HV2) is conserved among cross-hybridizing species, but variant in species-pairs that are reproductively isolated by post-pollination pre-fertilization reproductive barriers. In particular, variation in a tetrapeptide motif (XKPP) is systematically correlated with the presence of an interspecific reproductive barrier. Ka/Ks ratios are not informative at the infrageneric level, but the ratios reveal a clear signature of positive selection on two hypervariable domains (HV1 and HV2) when HD-AGPs from five solanaceous genera are compared. We propose that sequence divergence in the hypervariable domains of HD-AGPs reinforces sympatric speciation in incipient species that may have first diverged as a consequence of pollinator preferences or other ecological factors. Full article

(This article belongs to the Section Plant Molecular Biology)

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