Abstract
BackgroundBrassinosteroids (BRs) are a new group of plant hormones and play important roles in plant growth and development. However, little information is available if BRs could regulate spikelet development in rice (Oryza sativa L.) especially under soil-drying conditions. This study investigated whether and how BRs mediate the effect of soil-drying on spikelet differentiation and degeneration in rice. A rice cultivar was field-grown and exposed to three soil moisture treatments during panicle development, that is, well-watered (WW), moderate soil-drying (MD) and severe soil-drying (SD).ResultsCompared with the WW treatment, the MD treatment enhanced BRs biosynthesis in young panicles, increased spikelet differentiation and reduced spikelet degeneration. The SD treatment had the opposite effects. Changes in expression levels of key rice inflorescence development genes (OsAPO2 and OsTAW1), ascorbic acid (AsA) content, and activities of enzymes involved AsA synthesis and recycle, and amount of nonstructural carbohydrates (NSC) in young panicles were consistent with those in BRs levels, whereas hydrogen peroxide (H2O2) content showed opposite trend. Knockdown of the BRs synthesis gene OsD11 or application of a BRs biosynthesis inhibitor to young panicles markedly decreased OsAPO2 and OsTAW1 expression levels, BRs and AsA contents, activities of enzymes involved AsA synthesis and recycle, NSC amount in rice panicles and spikelet differentiation but increased the H2O2 content and spikelet degeneration compared to the control (the wide type or application of water). The opposite effects were observed when exogenous BRs were applied.ConclusionsThe results suggest that BRs mediate the effect of soil-drying on spikelet differentiation and degeneration, and elevated BRs levels in rice panicles promote spikelet development under MD by enhancing inflorescence meristem activity, AsA recycle and NSC partitioning to the growing panicles.
Highlights
Brassinosteroids (BRs) are a new group of plant hormones and play important roles in plant growth and development
The moderate soil-drying (MD) treatment markedly increased the amount of nonstructural carbohydrates (NSC) in young panicles, and the SD treatment significantly decreased it when compared with the WW treatment (Fig. 2b)
The NSC was most partitioned to the growing young panicle under the SD, intermediate under the MD, and the least in the WW treatment, suggesting that soil-drying during panicle development enhances the partitioning of assimilates from vegetative tissues to growing young panicles of rice
Summary
Brassinosteroids (BRs) are a new group of plant hormones and play important roles in plant growth and development. Little information is available if BRs could regulate spikelet development in rice (Oryza sativa L.) especially under soil-drying conditions. The panicle size, an important agronomic trait that makes valuable contributions to the grain productivity in rice (Oryza sativa L.), mainly depends on the number of spikelets on a panicle [1,2,3,4]. Reduction or elimination of spikelet degeneration to increase spikelet number is a ‘scientific conundrum’ and is critical in increasing grain yield of cereals. Great effort has been made to increase spikelets differentiation and reduction or elimination of spikelet degeneration in rice by agronomic, genetic and molecular approaches [3,4,5, 7,8,9,10]. The mechanism involved in spikelet differentiation and degeneration remains unclear
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