The RNA-binding protein RGGA is a sugar-responsive cofactor of the 5'-3' exonuclease XRN4 that post-transcriptionally meditates plant growth

Abstract

Sugar-regulated gene expression is a ubiquitous mechanism for carbohydrate allocation and utilization by keeping a balance among source and sink organs in plants. Previous studies have shown that excess sugar represses the expression of the genes implicated in photosynthesis and sugar metabolism. However, the mechanism is still largely unknown. Here, we found that the mutant of Arabidopsis RGGA, RGG repeats RNA-binding protein A coding gene, grew faster than wild type (Col-0) in MS medium. In rgga, mRNA half-live of the genes related to sucrose transport and metabolism, chlorophyll synthesis, root development as well as certain transcription factors was obviously longer than those of Col-0. Further study revealed that AtRGGA could interact with 5'-3' exonuclease AtXRN4, and guide it to the target mRNAs for their degradation. When AtRGGA is absent or its interaction domain is deleted, AtXRN4 self can't recognize the target mRNAs, which leads to a dramatically increase in transcript levels of the above gene subsets, and thus promotes the growth of Arabidopsis with exogenous sucrose supply. And only 5-day sucrose supply could trigger the vigorous growth of rgga. These findings suggest that the regulation of mRNA stability mediated by RGGA plays a critical role in sugar suppression, and implicates a possibility to unlock the growth potential by modulating sugar utilization at post-transcriptional level in plants.