Regulation of fruit and seed response to heat and drought by sugars as nutrients and signals

Yong-Hua Liu,Yong-Ling Ruan,Christina E Offler

doi:10.3389/fpls.2013.00282

Abstract

A large body of evidence shows that sugars function both as nutrients and signals to regulate fruit and seed set under normal and stress conditions including heat and drought. Inadequate sucrose import to, and its degradation within, reproductive organs cause fruit and seed abortion under heat and drought. As nutrients, sucrose-derived hexoses provide carbon skeletons and energy for growth and development of fruits and seeds. Sugar metabolism can also alleviate the impact of stress on fruit and seed through facilitating biosynthesis of heat shock proteins (Hsps) and non-enzymic antioxidants (e.g., glutathione, ascorbic acid), which collectively maintain the integrity of membranes and prevent programmed cell death (PCD) through protecting proteins and scavenging reactive oxygen species (ROS). In parallel, sugars (sucrose, glucose, and fructose), also exert signaling roles through cross-talk with hormone and ROS signaling pathways and by mediating cell division and PCD. At the same time, emerging data indicate that sugar-derived signaling systems, including trehalose-6 phosphate (T6P), sucrose non-fermenting related kinase-1 (SnRK), and the target of rapamycin (TOR) kinase complex also play important roles in regulating plant development through modulating nutrient and energy signaling and metabolic processes, especially under abiotic stresses where sugar availability is low. This review aims to evaluate recent progress of research on abiotic stress responses of reproductive organs focusing on roles of sugar metabolism and signaling and addressing the possible biochemical and molecular mechanism by which sugars regulate fruit and seed set under heat and drought.

Highlights

Food security is becoming a more and more important and urgent issue with increasing demand for enhancement of crop yield
A large body of evidence indicates that sugar metabolism and signaling play important regulatory roles in fruit and seed set and their subsequent development
It is clear that more direct molecular evidence is required to dissect the causal and consequential relationship between changes in sugar metabolism and other biochemical processes and associated phenotype

Summary

INTRODUCTION

Food security is becoming a more and more important and urgent issue with increasing demand for enhancement of crop yield. CENTRAL ROLES OF SUGAR METABOLISM IN FRUIT AND SEED SET UNDER HEAT AND DROUGHT Compared to vegetative organs, young reproductive organs are less competitive for nutrient acquisition, which may result from their distal location from source leaves, lower transport conductivities through plasmodesmata and differentiating phloem and their low INV activities (Ruan et al, 2012). This may decrease the sink strength of these reproductive organs leading to sucrose partitioning in favor of vegetative tissues (Sturm and Tang, 1999; Andersen et al, 2002) Consistent with this postulation, a heat tolerant tomato genotype exhibited higher CWIN and VIN activities in the flower and young fruit and a higher rate of sucrose import into young fruit than a heat sensitive genotype, which collectively contributed to higher fruit set under heat stress (Li et al, 2012). A high ability of sucrose partitioning to, and its degradation within, reproductive organs could be vital for fruit and seed set under heat and drought

SUCROSE METABOLISM CONTRIBUTES TO ANTIOXIDANT

Findings

CONCLUSION AND PERSPECTIVES