Characterization of an RNase Z nonsense mutation identified exclusively in environment-conditioned genic male sterile rice

The two-line hybrid system in rice is becoming more important and employs environment-conditioned genic male sterile (EGMS) lines sensitive to photoperiod (photoperiod-sensitive genic male sterile), temperature [temperature genic male sterile (TGMS)], or a combination of the two (photoperiod temperature genic male sterile). At least 18 EGMS genes have been mapped, and two cloned, but controversies exist. For example, three different genes were reported to underlie the TGMS trait in three independently identified progenitors, Annong S-1, Zhu 1S, and Guangzhan 63S, while another study demonstrated that the TGMS genes in Annong S-1 and Zhu 1S are allelic. In the present study, we confirmed the allelism of the three TGMS genes, which means there is a common TGMS gene(s) in these lines. Knowing there is an association between the mutant allele (RNZ m ) of a ribonuclease gene (RNZ) with the TGMS trait in Guangzhuan 63S, we then sequenced RNZ for 14 commercial EGMS and 21 non-EGMS lines, and we developed two derived cleaved amplified polymorphic sequence (dCAPS) markers to detect RNZ m alleles in 32 EGMS and 310 non-EGMS lines. The analyses showed that the RNZ m allele existed exclusively in EGMS lines; all non-EGMS lines contained the functional RNZ gc or RNZ tc allele. Furthermore, two segregating populations that included 2,429 individuals were developed by crossing Zhu 1S (RNZ m ) to two non-EGMS lines (both with RNZ tc ); examination of the segregation of male sterile and fertile plants indicated that the TGMS trait was under the control of a single gene; analysis of the markers revealed the RNZ m allele exclusively in TGMS plants and the RNZ tc allele only in non-TGMS plants in both populations. The dCAPS markers could therefore help select TGMS progeny in breeding programs, which will save time and labor, and improve breeding efficiency and accuracy.