Suppression or knockout of SaF/SaM overcomes the Sa-mediated hybrid male sterility in rice

Hybrids between the indica and japonica subspecies of rice （Oryza sativa） are usually sterile, which hinders utilization of heterosis in the inter-subspecific hybrid breeding. The complex locus Sa comprises two adjacently located genes, SaF and SaM, which interact to cause abortion of pollen grains carrying the japonica allele in japonica-indica hybrids. Here we showed that silencing of SaF or SaM by RNA interference restored male fertility in indica-japonica hybrids with heterozygous Sa. We further used clustered regularly interspaced short palindromic repeats （CRISPR）/Cas9-based genome editing to knockout the SaF and SaM alleles, respectively, of an indica rice line to create hybrid-compatible lines. The resultant artificial neutral alleles did not affect pollen viability and other agricultural traits, but did break down the reproductive barrier in the hybrids. We found that some rice lines have natural neutral allele Sa-n, which was compatible with the typical japonica or indica Sa alleles in hybrids. Our results demonstrate that SaF and SaM are required for hybrid male sterility, but are not essential for pollen development. This study provides effective approaches for the generation of hybrid-compatible lines by knocking out the Sa locus or using the natural Sa-n allele to overcome hybrid male sterility in rice breeding.

Salicylic acid-mediated plant defense： Recent developments, missing links, and future outlook

BACKGROUND： Plant pathogens are responsible for many of history＇s greatest famines. Understanding how plants defend themselves against pathogens is crucial to preventing future famines. Salicylic acid （SA）-mediated plant defense is a key defense pathway, which plants use to defend against biotrophic and hemi-biotrophic pathogens. As a master regulator of SA- mediated plant defense, NPR1 interacts with TGA and WRKY transcription factor families, individual members of which positively or negatively regulate plant defense. OBJECTIVE： In this review we describe the recent developments and predict future directions of research on the involvement of circadian rhythm-, autophagy-, and viral RNA silencing-related genes in SA-mediated plant defense on SA, on plant defense, the induction effects of PR proteins, and the mechanisms by which NPR1 regulates defense-related genes. METHODS： We performed an extensive search of current and past literature using the PubMed, Google Scholar, and Google search engines. Our search terms included： ＂SA-mediated plant defense,＂ and ＂NPR1 [AND] salicylic acid.＂ Other search terms, wildcards, and Boolean operators were paired with ＂NPRI＂ or ＂plant defense＂ as needed to research more detailed information related to specific topics covered within this review. We also used Google to search for, ＂economic impact citrus greening,＂ ＂aspirin,＂ ＂Irish potato famine,＂ and ＂rice blast,＂ among other terms, to gather background information on the history and impact of plant diseases, and the historical use of aspirin. RESULTS： Of 148 sources found, 132 were directly related to plant defense. The remaining sources are related to the historical and economic impact of plant diseases and the historical use and mechanism of action of aspirin or salicylate. All reviewed sources have been documented in the references section. CONCLUSION： The topic of salicylic acid-mediated plant defense is broad, and new research is expanding our understanding of this topic quickly. In this review, we give a basic overview of the historical economic impact of plant diseases, and how an understanding of SA-mediated plant defense can prevent future famines. We provide a basic overview of plant defense, then discuss how SA acts as a defense signaling molecule.We discuss how SA regulates NPR1, which goes on to activate expression of SA-related genes including PR genes. Later, we discuss current research topics, including the role of NPR1 and SA in autophagy, circadian rhythmicity, viral gene silencing, SA biosynthesis, and SAR. We also discuss the potential roles of PR proteins, other SA binding proteins, WRKY and TGA family transcription factors, Elongator, and ER transport proteins in plant defense. Finally, we discuss the potential future routes that research into this topic could take, in order to further our understanding of role SA plays in plant defense.