Abstract
Excessive nitrogen fertilizer application causes severe environmental degradation and drives up agricultural production costs. Thus, improving crop nitrogen use efficiency (NUE) is essential for the development of sustainable agriculture. Here, we characterized the roles of the MYB transcription factor OsMYB305 in nitrogen uptake and assimilation in rice. OsMYB305 encoded a transcriptional activator and its expression was induced by N deficiency in rice root. Under low-N condition, OsMYB305 overexpression significantly increased the tiller number, shoot dry weight and total N concentration. In the roots of OsMYB305-OE rice lines, the expression of OsNRT2.1, OsNRT2.2, OsNAR2.1, and OsNiR2 was up-regulated and 15NO3– influx was significantly increased. In contrast, the expression of lignocellulose biosynthesis-related genes was repressed so that cellulose content decreased, and soluble sugar concentration increased. Certain intermediates in the glycolytic pathway and the tricarboxylic acid cycle were significantly altered and NADH-GOGAT, Pyr-K, and G6PDH were markedly elevated in the roots of OsMYB305-OE rice lines grown under low-N condition. Our results revealed that OsMYB305 overexpression suppressed cellulose biosynthesis under low-nitrogen condition, thereby freeing up carbohydrate for nitrate uptake and assimilation and enhancing rice growth. OsMYB305 is a potential molecular target for increasing NUE in rice.
Highlights
Rice is a dietary staple for ∼50% of the global population (Godfray et al, 2010)
OsMYB305 was preferentially expressed in the young panicles, its transcripts were found in the roots, leaves, leaf sheaths, nodes and internodes (Supplementary Figures S1A,B)
Several studies have identified numerous transcription factors in rice that respond to low-nitrogen stress
Summary
Rice is a dietary staple for ∼50% of the global population (Godfray et al, 2010). Nitrogen (N) is the most important and limiting macronutrient for rice growth and productivity. Overexpression of the high-affinity nitrate transporter OsNRT2.3b increased N, Fe, and P uptake and significantly improved NUE and grain yield (Fan et al, 2016; Feng et al, 2017). Introduction of the ZmDof into rice significantly accelerated the photosynthesis and carbon flux toward N assimilation In this way, it improved N utilization and plant growth under low-N conditions (Kurai et al, 2011). OsMYB305 overexpression enhanced N uptake and assimilation, improved growth under low nitrogen conditions, reduced cellulose biosynthesis and altered carbon metabolism in rice. Our discoveries provide an empirical basis for the improvement of nitrogen uptake in rice by manipulating carbohydrate allocation between N assimilation and secondary cell wall biosynthesis
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