Molecular mapping of a rice gene conditioning thermosensitive genic male sterility using AFLP, RFLP and SSR techniques

The discovery and application of the thermosensitive genic male sterility (TGMS) system has great potential for revolutionizing hybrid seed production technology in rice. Use of the TGMS system in two-line breeding is simple, inexpensive, efficient, and eliminates the limitations associated with the cytoplasmic-genetic male sterility (CMS) system. An [F.sub.2] population developed from a cross between a TGMS indica mutant, TGMS-VN1, and a fertile indica line, CH1, was used to identify molecular markers linked to the TGMS gene and to subsequently determine its chromosomal location on the linkage map of rice. Bulk segregant analysis was performed using the AFLP technique. From the survey of 200 AFLP primer combinations, four AFLP markers (E2/M5-600, E3/M16-400, E5/M12-600, and E5/M12-200) linked to the TGMS gene were identified. All the markers were linked to the gene in the coupling phase. All except E2/M5-200 were found to be low-copy sequences. However, the marker E5/M12-600 showed polymorphism in RFLP analysis and was closely linked to the TGMS gene at a distance of 3.3 cM. This marker was subsequently mapped on chromosome 2 using doubled-haploid mapping populations derived from the crosses IR64 x Azucena and CT9993 x IR62666, available at IRRI, Philippines, and Texas Tech University, respectively. Linkage of microsatellite marker RM27 with the TGMS gene further confirmed its location on chromosome 2. The closest marker, E5/M12-600, was sequenced so that a PCR marker can be developed for the marker-assisted transfer of this gene to different genetic backgrounds. The new TGMS gene is tentatively designated as tms4(t).