Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2006
Publication Date: 2/1/2007
Citation: Gu, X.-Y., Foley, M.E. 2007. Epistatic interactions of three loci regulate flowering time under short and long daylengths in a backcross population of rice. Journal of Theoretical and Applied Genetics. 114:745-754. DOI:10.1007/s00122-006-0475-z. Interpretive Summary: Differentiation in the photoperiodic response of flowering has been key to the evolution and wide geographic distribution of wild, weedy, and cultivated rice. Rice is an essentially short-day plant, although all temperate and an overwhelming majority of tropical varieties exhibit only quantitative flowering responses to daylengths in excess of a critical period. We measured time to flowering and photoperiod sensitivity using hybrid F1 and a BC1 population developed from the cross of EM93-1 and SS18-2. SS18-2 is a weedy strain that is photoperiod sensitive and EM93-1 is a breeding line that is day-neutral. Quantitative trait loci analysis using the phenotypic data and a genetic map for the cross confirmed that three genes located on chromosomes 7 and 8 were responsible for the delayed flowering under long daylengths.
Technical Abstract: The short-day plant rice varies greatly in photoperiod sensitivity (PS) for flowering. The hybrid F1 from a cross between the day-neutral pure line EM93-1 and the weedy rice accession SS18-2 had stronger PS than SS18-2. Some BC1 (EM93-1/ F1) segregates were even more sensitive to photoperiod than the F1, as indicated by later flowering or no flowering after 250 d under a 14-h long daylength. A genome-wide scan identified the quantitative trait loci Se7.1, Se7.2, and Se8 for PS from the BC1 population, with all alleles that inhibit flowering derived from SS18-2. These three loci regulate time to flowering under long daylength through their main effects and di- and trigenic epistases. Under a 10-h short daylength, the regulation is through Se7.1 and Se8 main effects and digenic epistases involving all three loci. The short daylength not only nullified the main effect of Se7.2, but also changed its epistatic effects from inhibiting flowering under long daylength to promoting flowering. The epistases indicate that genes underlying the three PS loci work in the same pathway for control of flowering. Many non-flowered BC1s were the trigenic heterozygote; this suggests that the three PS loci are also involved in genetic control of critical daylength.