Abstract
Rice grain yield is a complex trait determined by three components: panicle number, grain number per panicle (GNPP) and grain weight. GNPP is the major contributor to grain yield and is crucial for its improvement. GNPP is determined by a series of physiological and biochemical steps, including inflorescence development, formation of rachis branches such as primary rachis branches and secondary rachis branches, and spikelet specialisation (lateral and terminal spikelets). The molecular genetic basis of GNPP determination is complex, and it is regulated by numerous interlinked genes. In this review, panicle development and the determination of GNPP is described briefly, and GNPP-related genes that influence its determination are categorised according to their regulatory mechanisms. We introduce genes related to rachis branch development and their regulation of GNPP, genes related to phase transition (from rachis branch meristem to spikelet meristem) and their regulation of GNPP, and genes related to spikelet specialisation and their regulation of GNPP. In addition, we describe other GNPP-related genes and their regulation of GNPP. Research on GNPP determination suggests that it is possible to cultivate rice varieties with higher grain yield by modifying GNPP-related genes.
Highlights
Rice is one of the most important food crops and feeds half of the world’s population [1,2]
LAX1, Ideal Plant Architecture 1 (IPA1)/WFP/OsSPL14, MOC1, Oryza sativa Homeobox1 (OSH1), Small Panicle (SPA), Short Panicle 1 (SP1), DENSE AND ERECT PANICLE1 (DEP1), OsNAC2 and Grain Number4-1 (GN4-1) positively regulate the number of rachis branches and the grain number per panicle (GNPP)
The above findings indicate that LARGER PANICLE (LP)/EP3, DENSE AND ERECT PANICLE3 (DEP3), PANICLE PHYTOMER 2 (PAP2)/OsMADS34, An-1, PROSTRATE GROWTH1 (PROG1) and DROUGHT AND SALT TOLERANCE (DST) negatively regulate the number of PRBs and SRBs and the GNPP in rice
Summary
Rice is one of the most important food crops and feeds half of the world’s population [1,2]. Because of reductions in available land and the increasing global population, increasing the rice grain yield per unit area is crucial for food security, in developing countries in Asia, such as in China and India [3]. Rice grain yield is primarily determined by three traits—grain number per panicle (GNPP), grain weight and number of panicles [4]. Because the rice grain yield per unit area is high, increasing the GNPP could further improve the grain yield [4,5,6]. We review progress in the molecular and genetic aspects of GNPP determination in rice
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