Delayed callose degradation restores the fertility of multiple P/TGMS lines in Arabidopsis

Photoperiod/temperature-sensitive genic male sterility(P/TGMS)is widely applied for improving crop production.Previous investigations using the reversible male sterile(rvms)mutant showed that slow development is a general mechanism for restoring fertility to P/TGMS lines in Arabidopsis.In this work,we isolated a restorer of rvms–2(res3),as the male sterility of rvms–2 was rescued by res3.Phenotype analysis and molecular cloning show that a point mutation in UPEX1 l in res3 leads to delayed secretion of callase A6 from the tapetum to the locule and tetrad callose wall degradation.Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis demonstrated that the tapetal transcription factor ABORTED MICROSPORES directly regulates UPEX1 expression,revealing a pathway for tapetum secretory function.Early degradation of the callose wall in the transgenic line eliminated the fertility restoration effect of res3.The fertility of multiple known P/TGMS lines with pollen wall defects was also restored by res3.We propose that the remnant callose wall may broadly compensate for the pollen wall defects of P/TGMS lines by providing protection for pollen formation.A cellular mechanism is proposed to explain how slow development restores the fertility of P/TGMS lines in Arabidopsis.

Characterization and fine mapping of RTMS10, a semi-dominant reverse thermo-sensitive genic male sterile locus in rice

The discovery and application of environment-sensitive genic male sterile(EGMS) rice germplasm provide an easy method for hybrid rice breeding and have made great contributions to hybrid rice production. Typically, the photoperiod-and thermosensitive GMS(P/TGMS) lines utilized in two-line hybrid systems are male sterile under long day or/and high temperature but fertile under short day or/and low temperature conditions. However, Yannong S(Yn S), a reverse TGMS(rTGMS) line, is sterile under low temperature(<29℃) and fertile under high temperature(>29.5℃). Here, we report a genetic study on the rTGMS trait in Yn S. Interestingly, the F1 plants of the cross between Yn S and a cultivar, L422, were male sterile at 22℃ and completely fertile at 27℃. Moreover, the segregation ratio of fertile and sterile individuals in Yn S/L422 F2 populations changed from 1:3.05 to 2.95:1 when the ambient temperature increased, showing that the rTGMS trait exhibits semidominance in Yn S. We further found a locus on chromosome 10, termed RTMS10, which controls the rTGMS trait in Yn S. We then finely mapped RTMS10 to a ~68 kb interval between markers ID13116 and ID1318 by Yn S/L422 BC6 F2 populations. A near iso-genic line(NIL) NL1 from the BC6 F3 generation was developed and the pollen of NL1 became abnormal from the meiosis stage under low temperature. In summary, we identified an rTGMS locus, RTMS10, and provided co-segregated markers, which could help to accelerate molecular breeding of rTGMS lines and better understand the rTGMS trait in rice.

Inheritance of the Pale—Green Leaf Marker and Sterility Trait in Photo—Thermo Sensitive Genic Male Sterile Rice

P/TGMS (photo-thermo sensitive genie male sterility) lines with pale-green leaf color have been developed in japonica rice. The marker trait is used as an assistant selection in the production of the two-lines system hybrid rice for the improvement of F, seed purity. A joint inheritance study of both leaf color and male sterility is presented for P/TGMS line with pale-green leaf color. The segregation ratios for leaf color in the F2 populations of the three crosses showed 13 : 3 and 15 : 1 at early and late sowing stages (April 26 and June 23) respectively, implying that the leaf color is controlled by two genes with fertility gene as dominant. Sterility level is higher in the early sowing stage than that in the late sowing. The inducement of male sterility is closely related to longer day-length and higher temperature at the developmental stages of young panicle. The genes to govern the leaf color and male fertility are inherited independently.

Development of the “Third-Generation” Hybrid Rice in China

Rice is a major cereal crop for China. The development of the ‘‘three-line" hybrid rice system based on cytoplasmic male sterility in the 1970 s(first-generation) and the ‘‘two-line" hybrid rice system based on photoperiod-and thermo-sensitive genic male-sterile lines(second-generation)in the 1980 s has contributed significantly to rice yield increase and food security in China. Here we describe the development and implementation of the ‘‘third-generation" hybrid rice breeding system that is based on a transgenic approach to propagate and utilize stable recessive nuclear male sterile lines, and as such, the male sterile line and hybrid rice produced using such a system is nontransgenic. Such a system should overcome the intrinsic problems of the ‘‘first-generation" and‘‘second-generation" hybrid rice systems and hold great promise to further boost production of hybrid rice and other crops.