Abstract
Exploring genetic methods to improve yield in grain crops such as rice (Oryza sativa) is essential to help meet the needs of the increasing population. Here, we report that rice ONAC096 affects grain yield by regulating leaf senescence and panicle number. ONAC096 expression increased rapidly in rice leaves upon the initiation of aging- and dark-induced senescence. Two independent T-DNA insertion mutants (onac096-1 and onac096-2) with downregulated ONAC096 expression retained their green leaf color during natural senescence in the field, thus extending their photosynthetic capacity. Reverse-transcription quantitative PCR analysis showed that ONAC096 upregulated genes controlling chlorophyll degradation and leaf senescence. Repressed OsCKX2 (encoding cytokinin oxidase/dehydrogenase) expression in the onac096 mutants led to a 15% increase in panicle number without affecting grain weight or fertility. ONAC096 mediates abscisic acid (ABA)-induced leaf senescence by upregulating the ABA signaling genes ABA INSENSITIVE5 and ENHANCED EM LEVEL. The onac096 mutants showed a 16% increase in grain yield, highlighting the potential for using this gene to increase grain production.
Highlights
Rice (Oryza sativa) is a major staple crop that feeds over one-third of the worldwide population [1]
Our findings suggest that downregulating ONAC096 increases tiller number by reducing OsCKX2 expression and delays leaf senescence by reducing the expression of chlorophyll degradation genes (CDGs) and senescence-associated genes (SAGs)
To further explore the roles of ONACs in regulating leaf senescence, we investigated the phylogenetic relationships between ONACs and seven Arabidopsis NAC proteins (ANACs) whose regulatory roles in leaf senescence have been determined (Figure S1)
Summary
Rice (Oryza sativa) is a major staple crop that feeds over one-third of the worldwide population [1]. Rice grain yield is mainly determined by the number of panicles per plant, grains per panicle, and weight of each grain [5]. Among these traits, one key factor in determining panicle number is tillering, which is coordinately regulated by many factors [6,7]. Mutants of rice nonyellow coloring (NYC3), encoding a plastid-localizing α/β hydrolase, exhibit a stay-green phenotype during dark-induced senescence [10]. The delayed leaf yellowing phenotype of stay-green (sgr) mutants under dark-induced and natural senescence conditions is due to a lack of magnesium-dechelating activity [12,13]
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