Identification of a Candidate restorer-of-fertility Gene Rf3 Encoding a Pentatricopeptide Repeat Protein for the Cytoplasmic Male Sterility in Soybean

Origin of CMS-PET1 cytotype in cultivated sunflower: A new insight

The vast majority of commercial sunflower hybrids worldwide are produced using cytoplasmic male sterility (CMS) of the PET1 type, resulting from the interspecific hybridization of Helianthus petiolaris with Helianthus annuus. Due to the fact that CMS-PET1 was not previously detected in wild sunflower, it was believed that this cytotype could arise during interspecific hybridization and is specific solely for cultivated sunflower. In this study, the open reading frame, orfH522, associated with the CMS-PET1 phenotype, was revealed for the first time in the 3'-flanking region of the mitochondrial atpA gene in wild H. annuus. An analysis of whole genome data from 1089 accessions showed that the frequency of occurrence of CMS-orfH522 in wild H. annuus populations is 3.58%, while in wild H. petiolaris populations, it is 1.26%. In general, the analysis demonstrated that PET1-CMS is a natural cytotype of H. annuus, and the appearance of the CMS phenotype in cultivated sunflowers is associated with the loss of stabilizing nuclear genes of fertility restorers, which occurred during interspecific hybridization. These data can explain the patterns of differential cytoplasmic and nuclear introgression occurring in wild sunflower and are useful for further evolutionary studies.

Current insights and advances into plant male sterility: new precision breeding technology based on genome editing applications

Plant male sterility (MS) represents the inability of the plant to generate functional anthers, pollen, or male gametes. Developing MS lines represents one of the most important challenges in plant breeding programs, since the establishment of MS lines is a major goal in F1 hybrid production. For these reasons, MS lines have been developed in several species of economic interest, particularly in horticultural crops and ornamental plants. Over the years, MS has been accomplished through many different techniques ranging from approaches based on cross-mediated conventional breeding methods, to advanced devices based on knowledge of genetics and genomics to the most advanced molecular technologies based on genome editing (GE). GE methods, in particular gene knockout mediated by CRISPR/Cas-related tools, have resulted in flexible and successful strategic ideas used to alter the function of key genes, regulating numerous biological processes including MS. These precision breeding technologies are less time-consuming and can accelerate the creation of new genetic variability with the accumulation of favorable alleles, able to dramatically change the biological process and resulting in a potential efficiency of cultivar development bypassing sexual crosses. The main goal of this manuscript is to provide a general overview of insights and advances into plant male sterility, focusing the attention on the recent new breeding GE-based applications capable of inducing MS by targeting specific nuclear genic loci. A summary of the mechanisms underlying the recent CRISPR technology and relative success applications are described for the main crop and ornamental species. The future challenges and new potential applications of CRISPR/Cas systems in MS mutant production and other potential opportunities will be discussed, as generating CRISPR-edited DNA-free by transient transformation system and transgenerational gene editing for introducing desirable alleles and for precision breeding strategies.

Male sterility and hybrid breeding in soybean

Hybrid breeding can help us to meet the challenge of feeding a growing world population with limited agricultural land. The demand for soybean is expected to grow; however, the hybrid soybean is still in the process of commercialization even though considerable progress has been made in soybean genome and genetic studies in recent years. Here, we summarize recent advances in male sterility-based breeding programs and the current status of hybrid soybean breeding. A number of male-sterile lines with cytoplasmic male sterility (CMS), genic-controlled photoperiod/thermo-sensitive male sterility, and stable nuclear male sterility (GMS) have been identified in soybean. More than 40 hybrid soybean varieties have been bred using the CMS three-line hybrid system and the cultivation of hybrid soybean is still under way. The key to accelerating hybrid soybean breeding is to increase the out-crossing rate in an economical way. This review outlines current problems with the hybrid soybean breeding systems and explores the current efforts to make the hybrid soybean a commercial success.