Overexpression of OsMYB305 in Rice Enhances the Nitrogen Uptake Under Low-Nitrogen Condition

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 <i>OsMYB305</i> in nitrogen uptake and assimilation in rice. <i>OsMYB305</i> encoded a transcriptional activator and its expression was induced by N deficiency in rice root. Under low-N condition, <i>OsMYB305</i> overexpression significantly increased the tiller number, shoot dry weight and total N concentration. In the roots of <i>OsMYB305</i>-OE rice lines, the expression of <i>OsNRT2.1</i>, <i>OsNRT2.2</i>, <i>OsNAR2.1</i>, and <i>OsNiR2</i> 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 <i>OsMYB305</i>-OE rice lines grown under low-N condition. Our results revealed that <i>OsMYB305</i> 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.