Abstract
Self-incompatibility (SI) is conserved among members of the Brassicaceae plant family. This trait is controlled epigenetically by the dominance hierarchy of the male determinant alleles. We previously demonstrated that a single small RNA (sRNA) gene is sufficient to control the linear dominance hierarchy in Brassica rapa and proposed a model in which a homology-based interaction between sRNAs and target sites controls the complicated dominance hierarchy of male SI determinants. In Arabidopsis halleri, male dominance hierarchy is reported to have arisen from multiple networks of sRNA target gains and losses. Despite these findings, it remains unknown whether the molecular mechanism underlying the dominance hierarchy is conserved among Brassicaceae. Here, we identified sRNAs and their target sites that can explain the linear dominance hierarchy of Arabidopsis lyrata, a species closely related to A. halleri. We tested the model that we established in Brassica to explain the linear dominance hierarchy in A. lyrata. Our results suggest that the dominance hierarchy of A. lyrata is also controlled by a homology-based interaction between sRNAs and their targets.
Highlights
Almost half of all angiosperms have a self-incompatibility (SI) system to avoid selffertilization which helps maintain genetic diversity within the species
We focused on the dominance–recessivity relationship between S20-SP11 and S13-SP11 (S20 > S13) because the only previously reported data about such relationships in A. lyrata pollen was that the expression of S13-SP11 is reduced in a S20S13 heterozygote, as revealed by gel blot analysis and in situ hybridization [19]
We suggest that AlSmi1-a is the only small RNA (sRNA) controlling the class IV > dominance hierarchy
Summary
Almost half of all angiosperms have a self-incompatibility (SI) system to avoid selffertilization which helps maintain genetic diversity within the species. Most Brassicaceae plants, including Arabidopsis lyrata, have SI systems ensuring that the plants’ sporophytic stigmas reject their own pollen grains This SI reaction is genetically controlled by a single multiallelic locus called the S locus, which contains the pollen and stigma determinant genes S-LOCUS PROTEIN 11 (SP11, called SCR) [1–3] and S-LOCUS RECEPTOR KINASE (SRK) [4,5], respectively. Class-II alleles follow a linear dominance hierarchy: S44 > S60 > S40 > S29 [10] This complex hierarchy is controlled by interactions between just two sRNAs, SP11 methylation inducer (Smi) and Smi, and their targets [11,12]. We previously proposed a model in which interactions between sRNAs and targets based on sequence similarity control the complicated linear dominance hierarchy of male SI determinants [12]. We identified sRNAs controlling the linear dominance hierarchy in A. lyrata, and we propose a homology-dependent model to explain the dominance–recessivity interaction of SP11 in A. lyrata
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