The selection of heterotic F1 hybrid varieties is a key agronomic strategy for improving crop yields,quality,and disease resistance(Bohra et al.,2016).Large-scale,low-cost hybrid seed production involves generating large populations of female plants,otherwise known as malesterile.Different techniques implying environmentally conditioned nuclear malesterility or mitochondria-driven cytoplasmic malesterility(CMS)have been used to this end,each with their own advantages and disadvantages(Kim and Zhang,2018).Because of its low cost and high purity,CMS hybrid breeding is by far the most widely used hybrid technology and has been implemented in many field and horticultural crops(Bohra et al.,2016).It usually relies on a three-component assembly involving a male-sterile CMS line,a fertility restorer line,and a maintainer one.Crosses between CMS and maintainer lines allow large-scale multiplication of female plants,whereas crosses with the restorer line produce heterotic malerestored hybrids that can thus set fruits(Figure 1).
APPLICABLE CROP DGMS TECHNOLOGY IN THE POST-HETEROSIS UTILIZATION ERA,The global population is predicted to grow by 25%and reach 10 billion by the mid-21st century(Hickey et al.,2019).To meet the food demands of the growing population with limited agricultural land and fresh water resources,greater and more consistent crop production under fluctuating climate conditions,including various environmental stresses,must be achieved by reducing resource inputs and minimizing environmental impacts(Bailey-Serres et al.t 2019).Thanks to the extensive use of semi-dwarf Green Revolution varieties and single-cross hybrids of major crops(e.g.,rice and maize),grain yield has increased steeply over the past 60 years(Figure 1A and 1B).For example。
As one of the most important crops, maize not only has been a source of the food, feed, and industrial feedstock for biofuel and bioproducts, but also became a model plant system for addressing fundamental questions in genetics. Male sterility is a very useful trait for hybrid vigor utilization and hybrid seed production. The identification and characterization of genic male-sterility (GMS) genes in maize and other plants have deepened our understanding of the molecular mechanisms controlling anther and pollen development, and enabled the development and efficient use of many biotechnology-based male-sterility (BMS) systems for crop hybrid breeding. In this review, we summarize main advances on the identification and characterization of GMS genes in maize, and con struct a putative regulatory network controlling maize anther and pollen development by comparative genomic analysis of GMS genes in maize, Arabidopsis, and rice. Furthermore, we discuss and appraise the features of more than a dozen BMS systems for propagating male-sterile lines and producing hybrid seeds in maize and other plants. Finally, we provide our perspectives on the studies of GMS genes and the development of novel BMS systems in maize and other plants. The continuous exploration of GMS genes and BMS systems will enhance our understanding of molecular regulatory networks controlling male fertility and greatly facilitate hybrid vigor utilization in breeding and field production of maize and other crops.
Xiangyuan WanSuowei WuZiwen LiZhenying DongXueli AnBiao MaYouhui TianJinping Li
The germplasm resources for the S-type malesterility is rich in maize and it is resistant to Bipolaris maydis race T and CI, but the commercial application of S-type cytoplasmic malesterility （CMS-S） in maize hybrid industry is greatly compromised because of its common fertility instability. Currently, the existence of multiple minor effect loci in specific nuclear genetic backgrounds was considered as the molecular mechanism for this phenomenon. In the present study, we evaluated the fertility segregation of the different populations with the fertility instable material FIL-H in two environments of Beijing and Hainan, China. Our results indicated that the fertility instability of FIL-H was regulated by multiple genes, and the expression of these genes was sensitive to environmental factors. Using RNA sequencing （RNA-seq） technology, transcriptomes of the sterile plants and partially fertile plants resulted from the backcross of FIL-HxJing 724 in Hainan were analyzed and 2 108 genes with different expression were identified, including 1 951 up-regulated and 157 down-regulated genes. The cluster analysis indicated that these differentially expressed genes （DEGs） might play roles in many biological processes, such as the energy production and conversion, carbohydrate metabolism and signal transduction. In addition, the path- way of the starch and sucrose metabolism was emphatically investigated to reveal the DEGs during the process of starch biosynthesis between sterile and partially fertile plants, which were related to the key catalytic enzymes, such as ADP-G pyrophosphorylase, starch synthase and starch branching enzyme. The up-regulation of these genes in the partially fertile plant may promote the starch accumulation in its pollen. Our data provide the important theoretical basis for the further exploration of the molecular mechanism for the fertility instability in CMS-S maize.
