Genetic Diversity of Weedy Rice and Its Potential Application as a Novel Source of Disease Resistance.

Weeds that infest crops are a primary factor limiting agricultural productivity worldwide. Weedy rice, also called red rice, has experienced independent evolutionary events through gene flow from wild rice relatives and de-domestication from cultivated rice. Each evolutionary event supplied/equipped weedy rice with competitive abilities that allowed it to thrive with cultivated rice and severely reduce yields in rice fields. Understanding how competitiveness evolves is important not only for noxious agricultural weed management but also for the transfer of weedy rice traits to cultivated rice. Molecular studies of weedy rice using simple sequence repeat (SSR), restriction fragment length polymorphism (RFLP), and whole-genome sequence have shown great genetic variations in weedy rice populations globally. These variations are evident both at the whole-genome and at the single-allele level, including Sh4 (shattering), Hd1 (heading and flowering), and Rc (pericarp pigmentation). The goal of this review is to describe the genetic diversity of current weedy rice germplasm and the significance of weedy rice germplasm as a novel source of disease resistance. Understanding these variations, especially at an allelic level, is also crucial as individual loci that control important traits can be of great target to rice breeders.

Advances in Understanding Mating Type Gene Organization in the Mushroom-Forming Fungus Flammulina velutipes.

The initiation of sexual development in the important edible and medicinal mushroom Flammulina velutipes is controlled by special genes at two different, independent, mating type (MAT) loci: HD and PR. We expanded our understanding of the F. velutipes mating type system by analyzing the MAT loci from a series of strains. The HD locus of F. velutipes houses homeodomain genes (Hd genes) on two separated locations: sublocus HD-a and HD-b. The HD-b subloci contained strain-specific Hd1/Hd2 gene pairs, and crosses between strains with different HD-b subloci indicated a role in mating. The function of the HD-a sublocus remained undecided. Many, but not all strains contained the same conserved Hd2 gene at the HD-a sublocus. The HD locus usually segregated as a whole, though we did detect one new HD locus with a HD-a sublocus from one parental strain, and a HD-b sublocus from the other. The PR locus of F. velutipes contained pheromone receptor (STE3) and pheromone precursor (Pp) genes at two locations, sublocus PR-a and PR-b. PR-a and PR-b both contained sets of strain-specific STE3 and Pp genes, indicating a role in mating. PR-a and PR-b cosegregated in our experiments. However, the identification of additional strains with identical PR-a, yet different PR-b subloci, demonstrated that PR subloci can recombine within the PR locus. In conclusion, at least three of the four MAT subloci seem to participate in mating, and new HD and PR loci can be generated through intralocus recombination in F. velutipes.