Plant cell wall is a complex polysaccharidic network and mainly consists of cellulose, hemicellulose, and pectins. The turgor pressure generated inside cell wall triggers cell growth. Therefore, cell wall also plays key roles during plant growth. Progress on cell wall biosynthesis and remodeling will promote crops breeding for the improvements on lodging resistance and yield. Besides cellulose synthesis occurring on the plasma membrane, noncellulosic polysaccharides are synthesized in the Golgi apparatus. However, the substrates, nucleotide sugars, are mainly produced in the cytosol. Plants have evolved nucleotide sugar transporter (NST) proteins for translocation of substrates from the cytoplasm to the Golgi lumen. Previous studies have shown that the defects on substrate synthesis lead to the impaired cell wall. It is unclear whether the defects on substrate supply would have the similar impacts due to the lack of genetic evidence.
The researchers from Yihua Zhou’s group, Institute of Genetics and Developmental Biology, CAS and Qian Qian’s group, China National Rice Research Institute, CAAS, have recently identified a cell-wall related transporter through characterization of a rice brittle culm mutant bc14. The bc14 mutant displayed reduced mechanical strength caused by decreased cellulose content and altered wall structure, and exhibits abnormalities in plant development. Map-based cloning and complementation test revealed that the mutant phenotypes result from a missense mutation in the gene Oryza sativa Nucleotide Sugar Transporter1 (OsNST1). OsNST1 was identified as a Golgi-localized transporter by analysis of a fluorescence-tagged OsNST1 expressed in rice protoplast cells and demonstration of uridine diphosphate glucose (UDP-glucose) transport activity via uptake assays in yeast. The decreased glucose content in matrix polysaccharides provided the direct support for its transport activity, as revealed by compositional sugar analyses in total and fractionated wall residues of wild-type and bc14 culms.
Identification of OsNST1 improved their understanding of how cell wall polysaccharide synthesis was regulated by Golgi NSTs in plants. Their study also provided the first genetic evidence for the long-term hypothesis on plant NSTs.
This work has been online published on Proceedings of the National Academy of Sciences of the USA (PNAS, DOI:/10.1073/pnas.1016144108) on March 7. Baocai Zhang, Xingling Liu and Qian Qian contribute equally as the first authors. This work was supported by grants from the Ministry of Agriculture of China for transgenic research (2008ZX08009-003) and the Knowledge Innovation Program of the Chinese Academy of Sciences (KSCX2-YW-G-033).
AUTHOR CONTACT:
ZHOU Yihua, Ph.D.
Institute of Genetics and Developmetnal Biology, Chinese Academy of Sciences, Beijing, China.
E-mail: yhzhou@genetics.ac.cn
