COEVOLUTION BETWEEN SEED DORMANCY AND AWN IN WEEDY RICE
Pipatpongpinyo, W., Feng, J., Ye, H. and Gu, X.-Y.
Agronomy, Horticulture, and Plant Science Department, South Dakota State University, Brookings, USA
Contact: Xing-You Gu, Xingyou.email@example.com
The seed dormancy (SD) and awn traits are both of adaptive significance in grass species. Awn, a needle-like appendage extended from the lemma of a floret, promotes seed dispersal and movement into soil, while SD regulates the timing of germination so that favorable genotypes could complete the life cycle in local ecosystems. This research aimed to address co-evolutionary relationship between the two adaptive traits using a genetic system developed from conspecific weedy and cultivated rice (Oryza sativa). The SD degree was correlated with the awn length (AL) in various ecotypes of weedy rice, with awned plants tended to have stronger dormancy. The correlation was accounted for by a few haplotype blocks, where a linkage disequilibrium (LD) between the SD and AL quantitative trait loci (QTL) could not be broken by >10 generations of phenotypic selection for delayed germination. Fine mapping of the SD8/AL8 haplotype delimited the LD to a genomic sequence of <1 Mb, which accounted for 27% and 64% of the variances for SD and AL, respectively, in a near-isogenic background. Both SD8 and AL8 interacted with the QTL SD1-2 in similar patterns, resulting in reduced dormancy or awn length. SD8 was further dissected from AL8. AL8 was collocated with RAE2/GAD1, a gene with pleiotropic effects on grain length, grain number and awn development in wild rice (O. rufipogon). However, AL8 has only the effect on AL, and differs in functional mutations from the RAE2/GAD1 alleles reported for the wild relative. In summary, this research provided evidence that the SD and awn traits co-evolved and tight linkage is a genetic mechanism underlying the coevolution. The research also suggested that some functional changes occurred to the linked genes during evolution.