Untitled

Abstract

Self-incompatibility is widespread in the grasses and it is proposed that the grasses share a common incompatibility mechanism that is distinct from those operating in the dicotyledonous species studied in great detail. Where good genetic data are available, all grass species appear to have an incompatibility mechanism controlled by two unlinked loci, S and Z. A putative S gene has been cloned from Phalaris coerulescens. This gene is characterized by two major domains: an allele specificity domain and a thioredoxin catalytic domain. A family of sequences with varying degrees of homology to this gene has been identified among 15 grass species covering all subfamilies of the Poaceae. These S-related sequences appear to be present in the grass family regardless of self-compatibility. Evidence is presented to show that at least one of the sequences is transcribed, suggesting a functional gene. In contrast to the high expression of the S gene in Phalaris pollen, expression of the related gene in the pollen (or anthers) of the grass species examined was so low that RNA gel blot analysis failed to display a significant signal. However, reverse transcription-based polymerase chain reaction (RT-PCR) successfully amplified the region corresponding to the S thioredoxin domain from 10 of the grass species. With grasses other than Phalaris, RT-PCR showed limited success in amplifying the region corresponding to the S variable portion at the 5' end of the Phalaris S gene. Sequencing of the PCR-amplified S thioredoxin region from wheat, barley, rye and Dactylis revealed that this is a highly conserved gene with 94-97% sequence similarity with the corresponding Phalaris S gene. The conservation of sequence and ubiquitous expression of the gene across the grass family strongly suggest that the S-related gene is carrying out a significant biological function in the Poaceae. On the basis of these findings, a model for the evolution of the S self-incompatibility gene in the grasses is proposed.

Thiol-based redox regulation in sexual plant reproduction: new insights and perspectives

“…In the plant Phalaris coerulescens , the SI model system is based on two multiallelic not-linked loci, called S and Z (Hayman and Richter, 1992 ; Li et al, 1997 ; Klaas et al, 2011 ). Locus S encodes a monocot-conserved protein exclusively expressed in mature pollen.…”

Fine-Mapping and Comparative Genomic Analysis Reveal the Gene Composition at theSandZSelf-incompatibility Loci in Grasses

“…Whereas our analysis was mainly focused on Lolium spp., it is commonly believed that the outbreeding nature of grass species can be attributed to the same SI system ( Li et al 1997 ; Baumann et al 2000 ). This belief is further supported by the high synteny observed of the S - and Z -locus and especially the presence of functional copies of the putative SI determinants in self-incompatible species belonging to the Poeae tribe ( L. perenne , L. multiflorum , and D. glomerata ), Triticeae tribe ( S. cereale ), and Oryzeae tribe ( O. longistaminata ).…”

“…The involvement of Ca 2+ -induced signaling transduction, protein phosphorylation, and the proteolysis pathway have been reported in preliminary studies ( Wehling et al 1994 ; Klaas et al 2011 ). The current knowledge suggests that self-incompatible species of the entire Poaceae family share the same SI system, similarly as all dicotyledonous species investigated at the molecular level belonging to the same family share the same SI system ( Li et al 1997 ; Baumann et al 2000 ). In perennial ryegrass ( L. perenne ), the S - and the Z -locus have been mapped to chromosomes 1 and 2, respectively, using genetic linkage mapping ( Thorogood et al 2002 ).…”

“…), and the Poeae ( Festuca pratensis Huds., Lolium perenne L., Lolium multiflorum Lam.) (see Li et al (1997) and Do Canto et al (2016) for a complete list). The SI system in grasses is gametophytically controlled and genetically governed by two multi-allelic and independent loci, S and Z ( Lundqvist 1954 ; Hayman 1956 ; Cornish et al 1979 ).…”

Molecular insights into self-incompatibility systems: From evolution to breeding

“…The two-locus ( S - Z ) GSI system in Poaceae is the most studied SI system in monocots ( Langridge and Baumann, 2008 ). The GSI system is controlled by two multiple-allelic loci, S and Z ( Li et al., 1997 ). Each locus contains two male and one female determinant, and SI occurs when the pollen S - and Z - genotypes are identical to the corresponding pistil genotypes ( Rohner et al., 2023 ).…”