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Grain weight and grain number, the two important yield traits, are mainly determined by grain size and panicle architecture in rice. Herein, we report the identification and functional analysis of OsSPL4 in panicle and grain development of rice. Using CRISPR/Cas9 system, two elite alleles of OsSPL4 were obtained, which exhibited an increasing number of grains per panicle and grain size, resulting in increase of rice yield. Cytological analysis showed that OsSPL4 could regulate spikelet development by promoting cell division. The results of RNA-seq and qRT-PCR validations also demonstrated that several MADS-box and cell-cycle genes were up-regulated in the mutation lines. Co-expression network revealed that many yield-related genes were involved in the regulation network of OsSPL4. In addition, OsSPL4 could be cleaved by the osa-miR156 in vivo, and the OsmiR156-OsSPL4 module might regulate the grain size in rice. Further analysis indicated that the large-grain allele of OsSPL4 in indica rice might introgress from aus varieties under artificial selection. Taken together, our findings suggested that OsSPL4 could be as a key regulator of grain size by acting on cell division control and provided a strategy for panicle architecture and grain size modification for yield improvement in rice. [ABSTRACT FROM AUTHOR]

Background: Salt stress and bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) are key limiting factors of rice (Oryza sativa L.) yields. Members of sucrose non-fermenting 1 (SNF1)-related protein kinase 2 (SnRK2), which is a family of plant-specific Ser/Thr kinases, are important components of signaling pathways involved in plant developmental processes and responses to stresses. There are 10 members of the SnRK2 family in rice; however, their functions are poorly understood, as are the underlying molecular mechanisms. Results: In this study, we found that OsSAPK9, which belongs to the SnRK2 family, positively regulated salt-stress tolerance and strain-specific resistance to bacterial blight in rice. RNA sequencing revealed that there were 404 and 1324 genes differentially expressed in OsSAPK9-RNAi in comparison with wild-type plants under salt-stress conditions and after Xoo inoculation, respectively, which participate in basic metabolic processes. In total, 65 common differentially expressed genes involved mainly in defense responses were detected both under salt-stress conditions and after Xoo inoculation. Moreover, in vivo and in vitro experiments demonstrated that OsSAPK9 forms a protein complex with the molecular chaperones OsSGT1 and OsHsp90, and transgenic plants overexpressing OsSGT1 exhibited decreased tolerances to salt stress and significantly increased resistance levels to bacterial blight. Thus, OsSAPK9 may function as a center node regulator of salt-stress responses and disease-resistance pathways through its interaction with OsSGT1 in rice. Conclusion: This study confirms that OsSAPK9 functions as a positive regulator of salt-stress responses and disease resistance through its interaction with OsSGT1 in rice. [ABSTRACT FROM AUTHOR]

Background: High soil salinity can cause significant losses in rice productivity worldwide, mainly because salt inhibits plant growth and reduces grain yield. To cope with environmental changes, plants have evolved several adaptive mechanisms that involve the regulation of many stress-responsive genes. Results: In this study, we identified OsSTAP1, which encodes an AP2/ERF-type transcription factor, was rapidly induced by ABA, ACC, salt, cold, and PEG treatments. OsSTAP1 is localized to the nucleus and acts as a transcriptional activator in plant cells. Compared with wild type, transgenic lines overexpressing OsSTAP1 exhibited increased tolerance to salt stress with higher SOD, POD, and CAT activities, and lower Na+/K+ ratios in the shoots. In addition, many other stress-responsive genes, including other ERF- and peroxidase-encoding genes, were upregulated in the OsSTAP1-overexpression lines. Conclusion: This study suggests that OsSTAP1 functions as an AP2/ERF transcriptional activator, and plays a positive role in salt tolerance by decreasing the Na+/K+ ratio and maintaining cellular redox homeostasis. [ABSTRACT FROM AUTHOR]