Molecular and Functional Insights into Sugar Transporters in Rice

doi:10.1016/j.rsci.2025.10.009

Abstract

Abstract:

Sugars are the main sources of energy and carbon for plants, making them crucial for various aspects of plant growth and development. Three prominent families of sugar transporters have been extensively researched: sucrose transporter, monosaccharide transporter, and sugars will eventually be exported transporter. The primary function of sugar transporters is to facilitate the movement of saccharide molecules, particularly sucrose and glucose, from cell to cell or from source tissues, such as leaves, to sink tissues like roots and developing seeds. Beyond mere transport, sugar transporters are integral to several biological and physiological processes in the plant. They are involved in phloem loading, which is critical for nutrient distribution throughout the plant, contribute to overall plant growth and development, and are essential in response to biotic (e.g., pathogen attack) and abiotic (e.g., drought or salinity) stresses. In this review, we provide a comprehensive summary and update on the functions of these sugar transporters, specifically in rice, and highlight the potential applications of gene editing technologies, which could be harnessed to enhance rice traits and improve yield.

Key words: sugar transporter, plant growth and development, biotic stress, abiotic stress, genome editing, rice

Kieu Anh Thi Phan, Juho Lee, Cong Danh Nguyen, Sang-Kyu Lee. Molecular and Functional Insights into Sugar Transporters in Rice[J]. Rice Science, 2026, 33(3): 309-326.

Figures/Tables 5

Fig. 1. Classification of sugar transporters and their distribution in plant cells. A, Three major categories of sugar transporters (SUTs, MSTs, and SWEETs), and the subfamilies of MSTs and their transported substrates, as well as MT, which is distinct from these transporter families and specifically transports maltose. B, Transporters mediated sugar transport on the plasma membrane and organelle membranes. The arrow directions indicate the export and import of sugars across the cell, as well as the movement of sugars across organelle membranes. ERD, Early response to dehydration 6-like transporters; Fru, Fructose; Glu, Glucose; INT, Inositol transporters; MSTs, Monosaccharide transporters; MT, Maltose transporter; pGlcT, Plastidic glucose translocators; PLT, Polyol/monosaccharide transporters; STP, Sugar transport proteins; Suc, Sucrose; SUTs, Sucrose transporters; SWEETs, Sugars Will Eventually be Exported Transporters; TST, Tonoplast sugar transporters; VGT, Vacuolar glucose transporters. The figure was created with BioRender.com.

Table 1. List of sugar transporter genes in plant growth and development and genome editing approaches.

Gene	Physiological function	Phenotype (knockout mutant)	Genome editing approach	Reference
SUTs/SUCs
OsSUT1	Seed/grain filling, phloem loading for the long-distance pathway, provide sugar for seed germination	Mild dwarf, sterile phenotype	CRISPR/Cas9	Hirose et al, 2010; Ishibashi et al, 2014; Wang et al, 2022
OsSUT2	Mediate embryo germination from endosperms	Reduction in tiller number, plant height, and grain weight	CRISPR/Cas9	Siao et al, 2011; Xiao et al, 2024
OsSUT3	Pollen development	-	-	Li Q P et al, 2023
MSTs
OsSTP3	Sugar accumulation for cell wall synthesis	-	-	Toyofuku et al, 2000
OsSTP4	Seed development during grain filling	-	-	Wang et al, 2007
OsSTP5	Pollen development	-	-	Ngampanya et al, 2003
OsSTP6	Role in source organs, abiotic stress response	Hypersensitivity to chilling	CRISPR/Cas9	Wang et al, 2008; Luo et al, 2024
OsSTP8	Pollen development	-	-	Mamun et al, 2006
OsSTP15	Cytokinin signal pathway in shoot base	Improve tiller number, enhance grain yield	CRISPR/Cas9	Li et al, 2024
OsSTP28	Nitrogen-determined tillering and yield formation	Improve tiller number, enhance grain yield	CRISPR/Cas9	Zhang et al, 2024
OsERD5	Tillering and yield	Mutant: reduce height; Overexpression: increase tiller number and grain yield	CRISPR/Cas9	Li et al, 2025
OsTST1	Transport sugar from source to sink tissues	Reduce height, delay rice heading and flowering, and decrease grain size	CRISPR/Cas9	Yang et al, 2023
OspGlcT2	Cell wall synthesis	-	-	Wang et al, 2006
SWEETs
OsSWEET1b	Leaf senescence mechanism	Leaf senescence, reduce rice yield	CRISPR/Cas9	Chen et al, 2024
OsSWEET3a	Young shoot development	Late germination, growth retardation	CRISPR/Cas9	Morii et al, 2020
OsSWEET4	Seed-filling stage	Empty caryopses	TALEN	Sosso et al, 2015
OsSWEET5	Regulate the crosstalk between sugar and auxin	Overexpression: growth retardation, senescence at the seedling stage	amiRNA	Zhou et al, 2014
OsSWEET11a	Pollen development and seed-filling	Impairment in grain-filling	CRISPR/Cas9 and TALEN	Jiang et al, 2013; Gao et al, 2018; Fei et al, 2021
OsSWEET11b	Biotic stress response	Overexpression: susceptibility to bacterial blight	dTALE	Wu et al, 2022
OsSWEET12	Biotic stress response	Overexpression: susceptibility to bacterial blight	TALEN (dTALE)	Li et al, 2013
OsSWEET13	Biotic stress response	No difference with wild type	CRISPR/Cas9	Zhou et al, 2015
OsSWEET14	Seed-filling stage	Increased plant height without yield penalty	CRISPR/Cas9 and TALEN	Li et al, 2012; Zeng et al, 2020
OsSWEET15	Seed-filling stage	Reduce pollen viability, high empty grains	CRISPR/Cas9 and TALEN	Streubel et al, 2013; Yang et al, 2018; Hu et al, 2023
MT
OsMEX1	Pollen of mature flowers	-	-	Ryoo et al, 2013

Table 1. List of sugar transporter genes in plant growth and development and genome editing approaches.

Gene	Physiological function	Phenotype (knockout mutant)	Genome editing approach	Reference
SUTs/SUCs
OsSUT1	Seed/grain filling, phloem loading for the long-distance pathway, provide sugar for seed germination	Mild dwarf, sterile phenotype	CRISPR/Cas9	Hirose et al, 2010; Ishibashi et al, 2014; Wang et al, 2022
OsSUT2	Mediate embryo germination from endosperms	Reduction in tiller number, plant height, and grain weight	CRISPR/Cas9	Siao et al, 2011; Xiao et al, 2024
OsSUT3	Pollen development	-	-	Li Q P et al, 2023
MSTs
OsSTP3	Sugar accumulation for cell wall synthesis	-	-	Toyofuku et al, 2000
OsSTP4	Seed development during grain filling	-	-	Wang et al, 2007
OsSTP5	Pollen development	-	-	Ngampanya et al, 2003
OsSTP6	Role in source organs, abiotic stress response	Hypersensitivity to chilling	CRISPR/Cas9	Wang et al, 2008; Luo et al, 2024
OsSTP8	Pollen development	-	-	Mamun et al, 2006
OsSTP15	Cytokinin signal pathway in shoot base	Improve tiller number, enhance grain yield	CRISPR/Cas9	Li et al, 2024
OsSTP28	Nitrogen-determined tillering and yield formation	Improve tiller number, enhance grain yield	CRISPR/Cas9	Zhang et al, 2024
OsERD5	Tillering and yield	Mutant: reduce height; Overexpression: increase tiller number and grain yield	CRISPR/Cas9	Li et al, 2025
OsTST1	Transport sugar from source to sink tissues	Reduce height, delay rice heading and flowering, and decrease grain size	CRISPR/Cas9	Yang et al, 2023
OspGlcT2	Cell wall synthesis	-	-	Wang et al, 2006
SWEETs
OsSWEET1b	Leaf senescence mechanism	Leaf senescence, reduce rice yield	CRISPR/Cas9	Chen et al, 2024
OsSWEET3a	Young shoot development	Late germination, growth retardation	CRISPR/Cas9	Morii et al, 2020
OsSWEET4	Seed-filling stage	Empty caryopses	TALEN	Sosso et al, 2015
OsSWEET5	Regulate the crosstalk between sugar and auxin	Overexpression: growth retardation, senescence at the seedling stage	amiRNA	Zhou et al, 2014
OsSWEET11a	Pollen development and seed-filling	Impairment in grain-filling	CRISPR/Cas9 and TALEN	Jiang et al, 2013; Gao et al, 2018; Fei et al, 2021
OsSWEET11b	Biotic stress response	Overexpression: susceptibility to bacterial blight	dTALE	Wu et al, 2022
OsSWEET12	Biotic stress response	Overexpression: susceptibility to bacterial blight	TALEN (dTALE)	Li et al, 2013
OsSWEET13	Biotic stress response	No difference with wild type	CRISPR/Cas9	Zhou et al, 2015
OsSWEET14	Seed-filling stage	Increased plant height without yield penalty	CRISPR/Cas9 and TALEN	Li et al, 2012; Zeng et al, 2020
OsSWEET15	Seed-filling stage	Reduce pollen viability, high empty grains	CRISPR/Cas9 and TALEN	Streubel et al, 2013; Yang et al, 2018; Hu et al, 2023
MT
OsMEX1	Pollen of mature flowers	-	-	Ryoo et al, 2013

Fig. 2. Diverse physiological roles of sugar transporters in different organs. A, OsSTP15 and OsSTP28 controls the tillering number through cytokinin and gibberellin signal pathways, respectively. The figure was created with BioRender.com. me, DNA methylation; GA2oxs, Gibberellin 2-oxidases. B, Several sugar transporters play roles in grain-filling stages and seed germination, but details have not been characterized. C, Sucrose is transported from the anther into the apoplast space via OsSWEET11a/b then arrived in the pollen through OsSUTs (predicted OsSUT1/3). Glucose and fructose can get inside the pollen through OsSTPs (predicted OsSTP5/8).

Fig. 3. Sugar transporters in response to biotic stress (plant-pathogen interactions). A, Xanthomonas oryzae pv. oryzae (Xoo) secretes transcription-activator-like (TAL) effectors that enhance the expression of specific sugar transporter genes (OsSWEET11a/13/14) during infection to promote disease. B, A mechanism that supports Rhizoctonia solani fungus occupies more sugar and facilitates the invasion of the pathogen into the host. C, Reduction in rice susceptibility to Meloidogyne graminicola caused by brown planthopper phloem-feeding. Left, Nymph brown planthopper (BPH) mechanism; Right, Gravid BPH oviposition mechanism. A solid arrow indicates regulation, while dotted arrows (dashed arrows) indicate an increase (upward arrow) or decrease (downward arrow) in concentration. The figure was created with BioRender.com.

Fig. 4. Sugar transporters in response to abiotic stress. Cross-talk of sugar transporters in rice plants against abiotic stresses. The external stresses activate defense signaling that includes sugar sensors, thus transducing signals into intracellular downstream pathways, including hormone stimulation, activation of target genes and proteins, and sugar translocation in response to stress. ABA, Abscisic acid; CK, Cytokinin; ERF, Ethylene response factor; ET, Ethylene; JA, Jasmonic acid; MSTs, Monosaccharide transporters; TF, Transcription factor; SUTs, Sucrose transporters (also known as SUCs); SWEETs, Sugar Will Eventually be Exported Transporters; pGlcT2, Plastidic glucose transporter 2. The figure was created with BioRender.com.

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