MicroRNA393 is involved in nitrogen-promoted rice tillering through regulation of auxin signal transduction in axillary buds.

Xiang Li,Mingyong Zhang,Caixia Gao,Kuaifei Xia,Zhen Liang,Kunling Chen

doi:10.1038/srep32158

Abstract

Rice tillering has an important influence on grain yield, and is promoted by nitrogen (N) fertilizer. Several genes controlling rice tillering, which are regulated by poor N supply, have been identified. However, the molecular mechanism associated with the regulation of tillering based on N supply is poorly understood. Here, we report that rice microRNA393 (OsmiR393) is involved in N-mediated tillering by decreasing auxin signal sensitivity in axillary buds. Expression analysis showed that N fertilizer causes up-regulation of OsmiR393, but down-regulation of two target genes (OsAFB2 and OsTB1). In situ expression analysis showed that OsmiR393 is highly expressed in the lateral axillary meristem. OsmiR393 overexpression mimicked N-mediated tillering in wild type Zhonghua 11 (ZH11). Mutation of OsMIR393 in ZH11 repressed N-promoted tillering, which simulated the effects of limited N, and this could not be restored by supplying N fertilizer. Western blot analysis showed that OsIAA6 was accumulated in both OsmiR393-overexpressing lines and N-treated wild type rice, but was reduced in the OsMIR393 mutant. Therefore, we deduced that N-induced OsmiR393 accumulation reduces the expression of OsTIR1 and OsAFB2, which alleviates sensitivity to auxin in the axillary buds and stabilizes OsIAA6, thereby promoting rice tillering.

Highlights

Is synthesized in the plant apex and is transported basipetally towards the root, which is known as polar auxin transport (PAT), and this inhibits bud outgrowth[12]
These results showed that OsmiR393 accumulation in rice is induced by high N fertilizer levels, similar to that observed in Arabidopsis[8]
These results demonstrate that N fertilizer and OsmiR393 overexpression promote outgrowth of axillary buds, and that OsmiR393 is involved in axillary bud formation

Summary

Introduction

Is synthesized in the plant apex and is transported basipetally towards the root, which is known as polar auxin transport (PAT), and this inhibits bud outgrowth[12]. The second messenger model suggests that auxin regulates the distribution and activity of CKs and SLs in the axillary meristem to control plant branching. Both of these models are supported by recent studies[16]. LAX1 is a regulator that controls axillary meristem initiation and/or maintenance during rice reproductive development[18]. Rice OsMIR393a and OsMIR393b showed different expression patterns, which suggests that conserved mechanisms were adopted in monocots and eudicots during plant development[32]. MiR393 was shown to target auxin (IAA) receptor genes TIR1 and AFB in different plants, including Arabidopsis and rice[31,33,34]. We present findings showing that N-induced rice tillering is caused by attenuating the sensitivity of tiller buds to auxin through microRNA OsmiR393-mediated auxin signal transduction

Methods

Results

Conclusion