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Progress towards elucidating the mechanisms of self-incompatibility in the grasses: further insights from studies in Lolium.

ABSTRACT: BACKGROUND AND SCOPE: Self-incompatibility (SI) in flowering plants ensures the maintenance of genetic diversity by ensuring outbreeding. Different genetic and mechanistic systems of SI among flowering plants suggest either multiple origins of SI or considerable evolutionary diversification. In the grasses, SI is based on two loci, S and Z, which are both polyallelic: an incompatible reaction occurs only if both S and Z alleles are matched in individual pollen with alleles of the pistil on which they alight. Such incompatibility is referred to as gametophytic SI (GSI). The mechanics of grass GSI is poorly understood relative to the well-characterized S-RNase-based single-locus GSI systems (Solanaceae, Rosaceae, Plantaginaceae), or the Papaver recognition system that triggers a calcium-dependent signalling network culminating in programmed cell death. There is every reason to suggest that the grass SI system represents yet another mechanism of SI. S and Z loci have been mapped using isozymes to linkage groups C1 and C2 of the Triticeae consensus maps in Secale, Phalaris and Lolium. Recently, in Lolium perenne, in order to finely map and identify S and Z, more closely spaced markers have been developed based on cDNA and repeat DNA sequences, in part from genomic regions syntenic between the grasses. Several genes tightly linked to the S and Z loci were identified, but so far no convincing candidate has emerged. RESEARCH AND PROGRESS: From subtracted Lolium immature stigma cDNA libraries derived from S and Z genotyped individuals enriched for SI potential component genes, kinase enzyme domains, a calmodulin-dependent kinase and a peptide with several calcium (Ca(2+)) binding domains were identified. Preliminary findings suggest that Ca(2+) signalling and phosphorylation may be involved in Lolium GSI. This is supported by the inhibition of Lolium SI by Ca(2+) channel blockers lanthanum (La(3+)) and verapamil, and by findings of increased phosphorylation activity during an SI response.

SUBMITTER: Klaas M

PROVIDER: S-EPMC3170160 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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Progress towards elucidating the mechanisms of self-incompatibility in the grasses: further insights from studies in Lolium.

Klaas Manfred M Yang Bicheng B Bosch Maurice M Thorogood Daniel D Manzanares Chloe C Armstead Ian P IP Franklin F C H FC Barth Susanne S

Annals of botany 20110727 4

<h4>Background and scope</h4>Self-incompatibility (SI) in flowering plants ensures the maintenance of genetic diversity by ensuring outbreeding. Different genetic and mechanistic systems of SI among flowering plants suggest either multiple origins of SI or considerable evolutionary diversification. In the grasses, SI is based on two loci, S and Z, which are both polyallelic: an incompatible reaction occurs only if both S and Z alleles are matched in individual pollen with alleles of the pistil o ...[more]

PMID: 21798860

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Project description:BackgroundPlant species have several mechanisms to avoid selfing such as dichogamy or a self-incompatibility response. Dichogamy in a single flower may reduce autogamy but, to avoid geitonogamy, plants must show flowering synchronization among all their flowers (i.e. synchronous dichogamy). It is hypothesized that one species would not simultaneously show synchronous dichogamy and self-incompatibility because they are redundant mechanisms to reduce selfing; however, this has not been accurately assessed.Methodology/principal findingsThis expectation was tested over two years in two natural populations of the closely related Mediterranean spurges Euphorbia boetica and E. nicaeensis, which completely avoid autogamy by protogyny at the cyathia level. Both spurges showed a high population synchrony (Z<79), and their inflorescences flower synchronously. In E. nicaeensis, there was no overlap among the cyathia in anthesis of successive inflorescence levels and the overlap between sexual phases of cyathia of the same inflorescence level was uncommon (4-16%). In contrast, E. boetica showed a high overlap among consecutive inflorescence levels (74-93%) and between sexual phases of cyathia of the same inflorescence level (48-80%). The flowering pattern of both spurges was consistent in the two populations and over the two successive years. A hand-pollination experiment demonstrated that E. nicaeensis was strictly self-compatible whereas E. boetica was partially self-incompatible.Conclusions/significanceWe propose that the complex pattern of synchronized protogyny in E. nicaeensis prevents geitonogamous crosses and, consequently, avoids selfing and inbreeding depression. In E. boetica, a high probability of geitonogamous crosses may occur but, alternatively, this plant escapes selfing through a self-incompatibility response. We posit that synchronous dichogamy and physiological self-incompatibility do not co-occur in the same species because each process is sufficiently effective in avoiding self-fertilization.

Dataset Information

Progress towards elucidating the mechanisms of self-incompatibility in the grasses: further insights from studies in Lolium.

Publications

Progress towards elucidating the mechanisms of self-incompatibility in the grasses: further insights from studies in Lolium.

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