BHLH Transcription Factor NtMYC2a Regulates Carbohydrate Metabolism during the Pollen Development of Tobacco (Nicotiana tabacum L. cv. TN90).

Shiquan Bian,Yongqiang Ding,Hongbo Zhang,Ning Yan,Zhongfeng Zhang,Chunkai Wang,Tian Tian,Yanhua Liu,Ning Fang

doi:10.3390/plants11010017

Abstract

Basic helix-loop-helix (bHLH) transcription factor MYC2 regulates plant growth and development in many aspects through the jasmonic acid (JA) signaling pathway, while the role of MYC2 in plant carbohydrate metabolism has not been reported. Here, we generated NtMYC2a-overexpressing (NtMYC2a-OE) and RNA-interference-mediated knockdown (NtMYC2a-RI) transgenic plants of tobacco (Nicotiana tabacum L. cv. TN90) to investigate the role of NtMYC2a in carbohydrate metabolism and pollen development. Results showed that NtMYC2a regulates the starch accumulation and the starch-sugar conversion of floral organs, especially in pollen. The RT-qPCR analysis showed that the expression of starch-metabolic-related genes, AGPs, SS2 and BAM1, were regulated by NtMYC2a in the pollen grain, anther wall and ovary of tobacco plants. The process of pollen maturation was accelerated in NtMYC2a-OE plants and was delayed in NtMYC2a-RI plants, but the manipulation of NtMYC2a expression did not abolish the pollen fertility of the transgenic plants. Intriguingly, overexpression of NtMYC2a also enhanced the soluble carbohydrate accumulation in tobacco ovaries. Overall, our results demonstrated that the bHLH transcription factor NtMYC2a plays an important role in regulating the carbohydrate metabolism during pollen maturation in tobacco.

Highlights

In flowering plants, pollen development is a complex and important physiological process which determines pollination, fertilization and hybrid seed production [1,2,3,4]
NtMYC2a-OE plants were stained black due to the over-accumulation of amylose, while overexpression of NtMYC2a and was delayed by the silencing of NtMYC2a. Those of the NtMYC2a-RI plants had over 50% stained yellow and the rest stained brown to black (Figure 2A,B). These findings suggest that the starch accumulation in pollen grains was enhanced by overexpression of NtMYC2a and was delayed by the silencing of NtMYC2a
In order to determine the regulation of starch metabolic gene expression by NtMYC2a, we examined the expression of three starch metabolic genes, including AGPs, SS2 and

Summary

Introduction

Pollen development is a complex and important physiological process which determines pollination, fertilization and hybrid seed production [1,2,3,4]. The pollen grains of angiosperms are derived from the microspore mother cells ( called pollen mother cells) in the pollen sac. This process involves multiple primary and secondary metabolism, among which the carbohydrate metabolism plays an important role [1,5,6]. As the richest storage carbohydrate in plants, starch provides energy for growth and development. Recent study revealed that male sterility may result from the disorder of starch synthesis and utilization in pollen grains [11]

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Conclusion