Golgi-localized membrane protein AtTMN1/EMP12 functions in the deposition of rhamnogalacturonan II and I for cell growth in Arabidopsis

• Published in: Journal of experimental botany Vol. 72; no. 10; pp. 3611 - 3629
• Main Authors: Hiroguchi, Akihiko, Sakamoto, Shingo, Mitsuda, Nobutaka, Miwa, Kyoko
• Format: Journal Article
• Language: English
• Published: UK Oxford University Press 04.05.2021
• Subjects: Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - genetics; Cell Wall; Golgi Apparatus; Membrane Proteins - genetics; Pectins - biosynthesis; Research Papers; cell elongation; rhamnogalacturonan II; cellular attachment; rhamnogalacturonan I; endomembrane protein (EMP); transmembrane nine protein (TMN); boron; pectin deposition; Golgi apparatus; Arabidopsis thaliana
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/erab065

Arabidopsis TMN1, a Golgi-localized membrane protein conserved among eukaryotes, is required for pectic polysaccharide deposition in cell walls for cell growth. Abstract Appropriate pectin deposition in cell walls is important for cell growth in plants. Rhamnogalacturonan II (RG-II) is a portion of pectic polysaccharides; its borate crosslinking is essential for maintenance of pectic networks. However, the overall process of RG-II synthesis is not fully understood. To identify a novel factor for RG-II deposition or dimerization in cell walls, we screened Arabidopsis mutants with altered boron (B)-dependent growth. The mutants exhibited alleviated disorders of primary root and stem elongation, and fertility under low B, but reduced primary root lengths under sufficient B conditions. Altered primary root elongation was associated with cell elongation changes caused by loss of function in AtTMN1 (Transmembrane Nine 1)/EMP12, which encodes a Golgi-localized membrane protein of unknown function that is conserved among eukaryotes. Mutant leaf and root dry weights were lower than those of wild-type plants, regardless of B conditions. In cell walls, AtTMN1 mutations reduced concentrations of B, RG-II specific 2-keto-3-deoxy monosaccharides, and rhamnose largely derived from rhamnogalacturonan I (RG-I), suggesting reduced RG-II and RG-I. Together, our findings demonstrate that AtTMN1 is required for the deposition of RG-II and RG-I for cell growth and suggest that pectin modulates plant growth under low B conditions.