Molecular mechanisms underlying the breakdown of gametophytic self-incompatibility.
The breakdown of self-incompatibility has occurred repeatedly throughout the evolution of flowering plants and has profound impacts on the genetic structure of populations. Recent advances in understanding of the molecular basis of self-incompatibility have provided insights into the mechanisms of its loss in natural populations, especially in the tomato family, the Solanaceae. In the Solanaceae, the gene that controls self-incompatibility in the style codes for a ribonuclease that causes the degradation of RNA in pollen tubes bearing an allele at the S-locus that matches either of the two alleles held by the maternal plant. The pollen component of the S-locus has yet to be identified. Loss of self-incompatibility can be attributed to three types of causes: duplication of the S-locus, mutations that cause loss of S-RNase activity, and mutations that do not cause loss of S-RNase activity. Duplication of the S-locus has been well studied in radiation-induced mutants but may be a relatively rare cause of the breakdown of self-incompatibility in nature. Point mutations within the S-locus that disrupt the production of S-RNase have been documented in natural populations. There are also a number of mutants in which S-RNase production is unimpaired, yet self-incompatibility is disrupted. The identity and function of these mutations is not well understood. Careful work on a handful of model organisms will enable population biologists to better understand the breakdown of self-incompatibility in nature.
Stone
J L
JL
Department of Biology, Colby College, Waterville, Maine 04901, USA. jstone@colby.edu
D020440:Gene Duplication; D017343:Genes, Plant; D005828:Genetics, Population; D009154:Mutation; D010802:Phylogeny; D011123:Polyploidy; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D019657:Solanaceae / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
D018749:RNA, Plant; D012260:Ribonucleases