Confirmation of a Gametophytic Self-Incompatibility in Oryza longistaminata

Abstract

Oryza longistaminata, a wild species of African origin, has been reported to exhibit self-incompatibility (SI). However, the genetic pattern of its SI remained unknown. In this study, we conducted self-pollination and reciprocal cross-pollination experiments to verify that O. longistaminata is a strictly self-incompatible species. The staining of pollen with aniline blue following self-pollination revealed that although pollen could germinate on the stigma, the pollen tube was unable to enter the style to complete pollination, thereby resulting in gametophytic self-incompatibility (GSI). LpSDUF247, a S-locus male determinant in the gametophytic SI system of perennial ryegrass, is predicted to encode a DUF247 protein. On the basic of chromosome alignment with LpSDUF247, we identified OlSS1 and OlSS2 as Self-Incompatibility Stamen candidate genes in O. longistaminata. Chromosome segment analysis revealed that the Self-Incompatibility Pistil candidate gene of O. longistaminata (OlSP) is a polymorphic gene located in a region flanking OlSS1. OlSS1 was expressed mainly in the stamens, whereas OlSS2 was expressed in both the stamens and pistils. OlSP was specifically highly expressed in the pistils, as revealed by RT-PCR and qRT-PCR analyses. Collectively, our observations indicate the occurrence of GSI in O. longistaminata and that this process is potentially controlled by OlSS1, OlSS2, and OlSP. These findings provide further insights into the genetic mechanisms underlying self-compatibility in plants.

Identification of the genes at S and Z reveals the molecular basis and evolution of grass self-incompatibility

“…Further supporting the role of the DUF247 genes, two DUF247 genes have been identified at the S-locus of the self-incompatible wild perennial rice species O. longistaminata ( Lian et al., 2021 ). Alongside the DUF247 gene, a gene encoding a short protein dubbed S-LOCUS PISTIL (SP) was also identified as a potential candidate gene within the O. longistaminata S-locus, as the SP gene was highly polymorphic and expressed at high levels in the pistil tissue ( Lian et al., 2021 ). As grass SI loci are predicted to have arisen from a duplication, we expected the nature of the genes present at the S- and Z-loci to be similar ( Lundqvist, 1962 ).…”

“…We predicted that these genes would be hypervariable if they were specificity determinants, and that at least one component would be extracellular. Previous studies have shown variability in SDUF2, SDUF3 and SP ( Manzanares et al., 2016 ; Lian et al., 2021 ). Indeed, alignments of DUF247 from available genomes (reconstructed in cases of frame shifting) showed hypervariability in two segments of each DUF247 member with limited variation elsewhere ( Supplementary Figure 3 ).…”

“…Previous experiments from ryegrass indicated that SDUF2 is present in pollen, although with some stigmatic expression ( Manzanares et al., 2016 ). Analysis of SDUF2 (named OlSS2 ) and SDUF3 ( OlSS1 ) and SP from O. longistaminata suggested SDUF3 was pollen-specific, SDUF2 expressed in both pollen and pistil, and SP strongly pistil-specific ( Lian et al., 2021 ). One limitation of the prior RNA-seq data analysis in ryegrass was the absence of an appropriate reference genome for identifying transcript abundance from highly variable genes.…”

“…Similarly, a DUF247 gene was located at the Z-locus in L. perenne , although variability of this gene was not probed ( Shinozuka et al., 2010 ; Thorogood et al., 2017 ). In a SI rice species, Oryza longistaminata , two DUF247 genes, and a small pistil-expressed protein (named SP) was present at the S-locus ( Lian et al., 2021 ). With the advent of a high-quality ryegrass genome, as well as abundant high-quality grass genomes now publicly available, we aimed to probe these regions in detail using prior knowledge from the above studies ( Frei et al., 2021 ; Nagy et al., 2022 ).…”

Genetic control of compatibility in crosses between wheat and its wild or cultivated relatives

“…However, some lines remained consistently crossable whatever the conditions suggesting that they could be useful for breeders willing to enlarge wheat diversity using related species usually poorly crossable with wheat such as rye (Bertin et al, 2009). (Baumann et al, 2000;Chen et al, 2017;Connor, 1979;Crain et al, 2020;Do Canto et al, 2016;Lian et al, 2021) Similarly, the effect of temperature on seed production in hybrids derived from crosses between wheat and diploid cultivated barley Hordeum vulgare or tetraploid wild-barley Hordeum bulbosum was also studied. Such crosses were initially performed to produce haploid wheat plants (Barclay, 1975).…”