OsSPL9 Regulates Grain Number and Grain Yield in Rice

Abstract

Rice grain yield consists of several key components, including tiller number, grain number per panicle (GNP), and grain weight. Among them, GNP is mainly determined by panicle branches and spikelet formation. In this study, we identified a gene affecting GNP and grain yield, OsSPL9, which encodes SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) family proteins. The mutation of OsSPL9 significantly reduced secondary branches and GNP. OsSPL9 was highly expressed in the early developing young panicles, consistent with its function of regulating panicle development. By combining expression analysis and dual-luciferase assays, we further confirmed that OsSPL9 directly activates the expression of RCN1 (rice TERMINAL FLOWER 1/CENTRORADIALIS homolog) in the early developing young panicle to regulate the panicle branches and GNP. Haplotype analysis showed that Hap3 and Hap4 of OsSPL9 might be favorable haplotypes contributing to high GNP in rice. These results provide new insights on high grain number breeding in rice.

Genetic control of branching patterns in grass inflorescences

“…Auxin flux through the epidermis converges on small regions of the IM, a process regulated by the auxin influx carrier ZmAUX1 (SvAUX1 in S. viridis ( Zhu et al, 2021a , 2021b ) and the auxin efflux carrier SISTER OF PINFORMED1 (SoPIN1/ZmPIN1D; O'Connor et al, 2014 ; Matthes et al, 2019 ; Figure 4 ). Loss-of-function mutations in SvAUX1 / SPARSE PANICLE1 reduce all orders of branching in the inflorescence, whether primary, secondary, tertiary, or higher, although the effect in maize is less striking than in S. viridis ( Huang et al, 2017 ; Zhu et al, 2021a , 2021b ). Vein patterning is controlled by PIN-FORMED1a (PIN1a) and PIN1b, which move auxin away from the local maxima and establish the position of vascular tissue ( O'Connor et al, 2014 ).…”

“…OsSPL18 binds to the promoter of DENSE and ERECT PANICLE1 (a G-protein γ subunit; Xing and Zhang, 2010 ; Liu et al, 2021 ) and activates it ( Yuan et al, 2019) , thereby increasing cell numbers. Mutations in OsSPL9 , the gene underlying the mutant LESS GRAIN NUMBER5 , exhibited less than half the number of secondary branches as wild-type indica lines, although primary branch number was unaffected ( Hu et al, 2021) .…”

“…In rice, OsMADS5 and OsMADS34 directly regulate RCN4 and accelerate the transition to spikelet production. Double mutants of OsMADS5 OsMADS34 or OsMADS34 RCN4 produce more branches, including secondary, tertiary, and even quaternary branches ( Zhu et al, 2021a , 2021b ). OsMADS34 promoters also contain SPL binding motifs, and OsMADS34 is directly regulated by OsSPL14 ( Wang et al, 2015 ).…”

The CRISPR/Cas9-Mediated Modulation of SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 8 in Alfalfa Leads to Distinct Phenotypic Outcomes

“…SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) proteins are a family of plant-specific transcription factors that possess a highly conserved zinc-containing DNA binding region termed the SBP-domain ( Yamasaki et al, 2004 ; Birkenbihl et al, 2005 ) and function in a partially overlapping manner in the regulation of an exceptionally diverse set of processes such as vegetative growth, response to abiotic stress and yield ( Yamasaki et al, 2009 ; Xing et al, 2013 ; Xu et al, 2016 ; Gao et al, 2018a ; Hu et al, 2021 ). Many SPL genes are targeted by microRNA156 (miR156), which is an abundant and highly conserved miRNA in plants that regulates the expression of its target genes through transcript cleavage and translational inhibition ( Gandikota et al, 2007 ; Gao et al, 2016 ).…”

Genetic and molecular pathways controlling rice inflorescence architecture

“…Meanwhile, overexpression of RCN1 in the OsSPL14 knock-down plants can rescue the secondary branch defects, suggesting that OsSPL14 acts upstream of RCN1 in controlling conversion of BM to SM ( Wang et al., 2015 ). Recently, OsSPL9 has been identified as a positive regulator of secondary branch number, which directly activates RCN1 expression ( Hu et al., 2021a ), implying that SPLs mediate meristem identity conversion may not always through MADS-box genes.…”