OsRRM, an RNA-Binding Protein, Modulates Sugar Transport in Rice (Oryza sativa L.).

Derui Liu,Lina Xu,Jiping Gao,Sukui Jin,Shuwen Jia,Wei Wang

doi:10.3389/fpls.2020.605276

Abstract

Sugar allocation between vegetative and reproductive tissues is vital to plant development, and sugar transporters play fundamental roles in this process. Although several transcription factors have been identified that control their transcription levels, the way in which the expression of sugar transporter genes is controlled at the posttranscriptional level is unknown. In this study, we showed that OsRRM, an RNA-binding protein, modulates sugar allocation in tissues on the source-to-sink route. The OsRRM expression pattern partly resembles that of several sugar transporter and transcription factor genes that specifically affect sugar transporter gene expression. The messenger RNA levels of almost all of the sugar transporter genes are severely reduced in the osrrm mutant, and this alters sugar metabolism and sugar signaling, which further affects plant height, flowering time, seed size, and starch synthesis. We further showed that OsRRM binds directly to messenger RNAs encoded by sugar transporter genes and thus may stabilize their transcripts. Therefore, we have uncovered the physiological function of OsRRM, which sheds new light on sugar metabolism and sugar signaling.

Highlights

Because the stem is the vital hub for sugar transport from the leaves to sink tissues and sugar transporters mediate the transport of sugar from leaves to stem and from stem to seeds, we further examined the messenger RNAs (mRNAs) levels of sugar transport-related genes including OsSUT 1-4, the monosaccharide transporters OsMST6 and 8, and OsTMT1 and 2 in stems of osrrm and wild type (WT) plants at the beginning of the heading stage
We found that the highest level of OsRRM expression occurs in stems and leaves, and that OsRRM expression is higher in leaf sheaths and immature seeds than it is in panicles and roots
Because osrrm mutant plants phenocopy several monosaccharide or disaccharide transporter mutants, and the transcript levels of these sugar transport-related genes were reduced in the osrrm mutant (Figure 4C), we considered that OsRRM may be involved in posttranscriptional control of these sugar transporter genes

Summary

Introduction

Excess assimilated carbon is stored in the form of starch either in leaves, as has been shown in Arabidopsis (Zeeman and Ap Rees, 1999), or in the sink tissues after conversion from soluble sugars, such as sucrose, that are transported from the photosynthetic tissues in cereals (Nakano et al, 1995). Sucrose can be hydrolyzed into the monosaccharides glucose and fructose. These three types of sugar are widely distributed to heterotrophic sink tissues (Rees, 1994). Sugars are needed for cell wall biosynthesis (Carpita, 1996) and for the synthesis of other carbohydrate polymers, such as starch (Hanes, 1940). Maintaining the homeostasis of sugar content and allocation is vital to plant growth and development (Riesmeier et al, 1993, 1994; Eveland and Jackson, 2012; Lastdrager et al, 2014)

Methods

Results

Conclusion