Rice SUT and SWEET Transporters.

Liping Niu,Zhenjia Tang,Zhi Hu,Dechun Zhang,Fang Yang,Yanming Zhang,Yibing Hu

doi:10.3390/ijms222011198

Abstract

Sugar transporters play important or even indispensable roles in sugar translocation among adjacent cells in the plant. They are mainly composed of sucrose–proton symporter SUT family members and SWEET family members. In rice, 5 and 21 members are identified in these transporter families, and some of their physiological functions have been characterized on the basis of gene knockout or knockdown strategies. Existing evidence shows that most SUT members play indispensable roles, while many SWEET members are seemingly not so critical in plant growth and development regarding whether their mutants display an aberrant phenotype or not. Generally, the expressions of SUT and SWEET genes focus on the leaf, stem, and grain that represent the source, transport, and sink organs where carbohydrate production, allocation, and storage take place. Rice SUT and SWEET also play roles in both biotic and abiotic stress responses in addition to plant growth and development. At present, these sugar transporter gene regulation mechanisms are largely unclear. In this review, we compare the expressional profiles of these sugar transporter genes on the basis of chip data and elaborate their research advances. Some suggestions concerning future investigation are also proposed.

Highlights

As a group of positive sugar transporters, they are extremely important for the acquisition of sucrose from the intercellular apoplast outside of the cell into the cytosol, when no plasmodesma exists between adjacent cells, and a membrane transporter or channel is the only pathway for material exchange
We focus on the two classes of sugar transporters in rice and review advances in the characterization of their physiological roles and molecular mechanisms
It seems that the importance of the characterized SWEET genes in rice growth and development conform to the following order: OsSWEET4 > OsSWEET11

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. As a group of positive sugar transporters, they are extremely important for the acquisition of sucrose from the intercellular apoplast outside of the cell into the cytosol, when no plasmodesma exists between adjacent cells, and a membrane transporter or channel is the only pathway for material exchange These circumstances include the maternal–filial interface in the seed, the embryo–endosperm interface after the initial stage of seed development, and probably the pollen tube–pistil interface during the pollen tube fast growth stage after pollination [8,9,10]. SWEET is a class of passive sugar transporters that transport oligosaccharides such as glucose or sucrose across the membrane along their concentration gradients This property attributes them with the ability to import or export sugar in or out of a cell. Unlike the plant-specific SUT, SWEETs are present in both plants and animals [17] Their homologs in prokaryotes, SemiSWEETs, which transport sucrose and glucose, were identified in both bacteria and archaea [18]. Gaining a full understanding of the functions of these sugar transporters is challenging, with respect to gene regulation mechanisms

Physiological Functions of Rice SUT Sucrose Transporters

Rice SUT Gene Regulations

Physiological Functions of Rice SWEETs

SWEETs Interaction with Pathogens

SWEETs Response to Abiotic Stress and Regulation

Concluding Remarks