The E3 ubiquitin ligase CSIT1 regulates critical sterility-inducing temperature by ribosome-associated quality control to safeguard two-line hybrid breeding in rice

Two-line hybrid breeding can fully utilize heterosis in crops.In thermo-sensitive genic male sterile(TGMS)lines,low critical sterility-inducing temperature(CSIT)is vital to safeguard the production of two-line hybrid seeds in rice(Oryza sativa),but the molecular mechanism determining CSIT is unclear.Here,we report the cloning of CSIT1,which encodes an E3 ubiquitin ligase,and show that CSIT1 modulates the CSIT of thermo-sensitive genic male sterility 5(tms5)-based TGMS lines through ribosome-associated quality control(RQC).Biochemical assays demonstrated that CSIT1 binds to the 80S ribosomes and ubiquitinates abnormal nascent polypeptides for degradation in the RQC process.Loss of CSIT1 function inhibits the possible damage of tms5 to the ubiquitination system and protein translation,resulting in enhanced accumulation of anther-related proteins such as catalase to suppress abnormal accumulation of reactive oxygen species and premature programmed cell death in the tapetum,thereby leading to a much higher CSIT in the tms5-based TGMS lines.Taken together,our findings reveal a regulatory mechanism of CSIT,providing new insights into RQC and potential targets for future two-line hybrid breeding.

The Utilization of HB-red Flower in Hybrid Cotton Breeding

The HB-red flower trait came from the filial generation of the interspecific cross of upland cotton(Gossypium hirsutum L.) and G.bickii.It exhibits pink petals and filaments,with a large

A historical review of hybrid rice breeding

The development of germplasm resources and advances in breeding methods have led to steady increases in yield and quality of rice (Oryza sativa L.). Three milestones in the recent history of rice breeding have contributed to these increases: dwarf rice breeding, hybrid rice breeding, and super rice breeding. On the 50th anniversary of the success of three-line hybrid rice,we highlight important scientific discoveries in rice breeding that were made by Chinese scientists and summarize the broader history of the field. We discuss the strategies that could be used in the future to optimize rice breeding further in the hope that China will continue to play a leading role in international rice breeding.

Breeding of New Large Cocoon and Hypersilkgeneous Tussah Varieties with Eurytopicity

The new tussah varieties have been bred by selecting large,high quality and midterm based on the indexes of high cocoon shell rate and high stress resistance. In the meantime,whole cocoon weight,hatchability and other economic parameters were considered in new variety breeding. Through 14 generations of hybrid breeding for over 7 years,two new tussah varieties had been successfully obtained. The breeding results of DW were as follows: the 1 000-cocoon weight was11. 57 kg; the whole cocoon weight was 12. 06 g; the cocoon shell rate was 12. 22%; and the larval-pupal integrated survival rate was 95. 87%. The breeding results of GH were as follows: the 1 000-cocoon weight was 11. 52 kg; the whole cocoon weight was 11. 95 g; the cocoon shell rate was 12. 66%; and the larval-pupal integrated survival rate was 90. 37%.

The essential roles of sugar metabolism for pollen development and male fertility in plants

Sugar metabolism plays an essential role in plant male reproduction. Defects in sugar metabolism during anther and pollen development often result in genic male sterility(GMS). In this review, we summarize the recent progresses of the sugar metabolism-related GMS genes and their roles during plant anther and pollen development, including callose wall and primexine formation, intine development, pollen maturation and starch accumulation, anther dehiscence, and pollen germination and tube growth. We predict 112 putative sugar metabolic GMS genes in maize based on bioinformatics and RNA-seq analyses, and most of them have peak expression patterns during middle or late anther developmental stages.Finally, we outline the potential applications of sugar metabolic GMS genes in crop hybrid breeding and seed production. This review will deepen our understanding on sugar metabolic pathways in controlling pollen development and male fertility in plants.

Identification of no pollen 1 provides a candidate gene for heterosis utilization in foxtail millet(Setaria italica L.)

Male sterility is a common biological phenomenon in plant kingdom and has been used to generate male-sterile lines, which are important genetic resources for commercial hybrid seed production. Although increasing numbers of male-sterility genes have been identified in rice(Oryza sativa) and Arabidopsis(Arabidopsis thaliana), few male-sterility-related genes have been characterized in foxtail millet(Setaria italica). In this study, we isolated a male-sterile ethyl methanesulfonate-generated mutant in foxtail millet, no pollen 1(sinp1), which displayed abnormal Ubisch bodies, defective pollen exine and complete male sterility. Using bulk segregation analysis, we cloned SiNP1 and confirmed its function with CRISPR/Cas9 genome editing. SiNP1 encoded a putative glucose-methanol-choline oxidoreductase.Subcellular localization showed that the SiNP1 protein was preferentially localized to the endoplasmic reticulum and was predominantly expressed in panicle. Transcriptome analysis revealed that many genes were differentially expressed in the sinp1 mutant, some of which encoded proteins putatively involved in carbohydrate metabolism, fatty acid biosynthesis, and lipid transport and metabolism, which were closely associated with pollen wall development. Metabolome analysis revealed the disturbance of flavonoids metabolism and fatty acid biosynthesis in the mutant. In conclusion, identification of SiNP1 provides a candidate male-sterility gene for heterosis utilization in foxtail millet and gives further insight into the mechanism of pollen reproduction in plants.

Understanding the genetic and molecular constitutions of heterosis for developing hybrid rice

The wide adoption of hybrid rice has greatly increased rice yield in the last several decades.The utilization of heterosis facilitated by male sterility has been a common strategy for hybrid rice development.Here,we summarize our efforts in the genetic and molecular understanding of heterosis and male sterility together with the related progress from other research groups.Analyses of F1 diallel crosses show that strong heterosis widely exists in hybrids of diverse germplasms,and inter-subspecific hybrids often display higher heterosis.Using the elite hybrid Shanyou 63 as a model,an immortalized F2 population design is conducted for systematic characterization of the biological mechanism of heterosis,with identification of loci controlling heterosis of yield and yield component traits.Dominance,overdominance,and epistasis all play important roles in the genetic basis of heterosis;quantitative assessment of these components well addressed the three classical genetic hypotheses for heterosis.Environment-sensitive genic male sterility(EGMS)enables the development of two-line hybrids,and long noncoding RNAs often function as regulators of EGMS.Inter-subspecific hybrids show greatly reduced fertility;the identification and molecular characterization of hybrid sterility genes offer strategies for overcoming inter-subspecific hybrid sterility.These developments have significant implications for future hybrid rice improvement using genomic breeding.

A straight-forward seed production technology system for foxtail millet(Setaria italica)

For autogamous crops, a precondition for using heterosis is to produce sufficient pure male-sterile female parents that can be used to produce hybrid seeds. To date, cytoplasmic male sterility(CMS)and environment-sensitive genic male sterility(EGMS) have been used commercially to exploit heterosis for autogamous species. However, neither CMS nor EGMS has been established for foxtail millet(Setaria italica). Here, we report on the establishment and application of a seed production technology(SPT) system for this crop.First, we established a Ds Red-based SPT system,but found that it was unsuitable because it required the use of a fluorescent device for seed sorting. Instead, we constructed an SPT system with de novo betalain biosynthesis as the selection marker. This allowed us to distinguish transgenic seeds with the naked eye, thereby facilitating the identification of SPT maintainer line seeds. In this system, a seed sorter was not required to obtain sufficient seeds. The key point of the strategy is that the seed pool of the SPT maintainer line is propagated by artificial identification and harvesting of male-fertile individuals in the field, and the male-sterile line seed pool for hybrid production is produced and propagated by free pollination of male-sterile plants with the SPT maintainer line. In a field experiment, we obtained 423.96 kg male-sterile line seeds per acre,which is sufficient to plant 700.18 acres of farmland for hybrid seed production or male-sterile line reproduction. Our study therefore describes a powerful tool for hybrid seed production in foxtail millet, and demonstrates how the SPT system can be used for a small-grained crop with high reproduction efficiency.

MS1 is essential for male fertility by regulating the microsporocyte cell plate expansion in soybean

Male sterility is an essential trait in hybrid seed production,especially for monoclinous and autogamous food crops.Soybean male-sterile ms1 mutant has been known for more than 50 years and could be instrumental in making hybrid seeds.However,the gene responsible for the male-sterile phenotype has remained unknown.Here,we report the map-based cloning and characterization of the MS1 gene in soybean.MS1 encodes a kinesin protein and localizes to the nucleus,where it is required for the male meiotic cytokinesis after telophase Ⅱ.We further substantiated that MS1 colocalizes with microtubules and is essential for cell plate formation in soybean male gametogenesis through immunostaining.Both ms1 and CRISPR/Cas9 knockout mutants show complete male sterility but are otherwise phenotypically normal,making them perfect tools for producing hybrid seeds.The identification of MS1 has the practical potential for assembling the sterility system and speeding up hybrid soybean breeding.

Methylesterification of cell-wall pectin controls the diurnal flower-opening times in rice

Flowers are the core reproductive organ of plants, and flowering is essential for cross-pollination. Diurnal flower-opening time is thus a key trait influencing reproductive isolation, hybrid breeding, and thermostability in plants. However, the molecular mechanisms controlling this trait remain unknown. Here, we report that rice Diurnal Flower Opening Time 1 (DFOT1) modulates pectin methylesterase (PME) activity to regulate pectin methylesterification levels of the lodicule cell walls, which affect lodicule swelling to control diurnal flower-opening time. DFOT1 is specifically expressed in the lodicules, and its expression gradually increases with the approach to flowering but decreases with flowering. Importantly, a knockout of DFOT1 showed earlier diurnal flower opening. We demonstrate that DFOT1 interacts directly with multiple PMEs to promote their activity. Knockout of PME40 also resulted in early diurnal flower opening, whereas overexpression of PME42 delayed diurnal flower opening. Lower PME activity was observed to be associated with higher levels of pectin methylesterification and the softening of cell walls in lodicules, which contribute to the absorption of water by lodicules and cause them to swell, thus promoting early diurnal flower opening. Higher PME activity had the opposite effect. Collectively, our work uncovers a molecular mechanism underlying the regulation of diurnal flower-opening time in rice, which would help reduce the costs of hybrid breeding and improve the heat tolerance of flowering plants by avoiding higher temperatures at anthesis.