Rice Sucrose Partitioning Mediated by a Putative Pectin Methyltransferase and Homogalacturonan Methylesterification

Abstract

Homogalacturonan (HG) is the main component of pectins. HG methylesterification has recently emerged as a key determinant controlling cell attachment, organ formation, and phyllotaxy. However, whether and how HG methylesterification affects intercellular metabolite transport has rarely been reported. Here, we identified and characterized knockout mutants of the rice () gene encoding a putative pectin methyltransferase. mutants exhibit a remarkable decrease in the degree of methylesterification of HG in the culm-sieve element cell wall and a markedly reduced grain yield. The culm of mutant plants contains excessive sucrose (Suc), and aCO feeding experiment showed that the Suc overaccumulation in the culm was caused by blocked Suc translocation. These and other findings demonstrate that OsQUA2 is essential for maintaining a high degree of methylesterification of HG in the rice culm-sieve element cell wall, which may be critical for efficient Suc partitioning and grain filling. In addition, our results suggest that the apoplastic pathway is involved in long-distance Suc transport in rice. The identification and characterization of the gene and its functionality revealed a previously unknown contribution of HG methylesterification and provided insight into how modification of the cell wall regulates intercellular transport in plants.

Rice Putative Methyltransferase Gene OsPMT16 Is Required for Pistil Development Involving Pectin Modification

“…When cells differentiate, they need to communicate closely with surrounding cells (Kepinski, 2006). In the QUA2/TSD2 deletion mutant, abnormalities in cell adhesion in the hypocotyl occurred, indicating the possibility of an abnormality in intercellular communication (Qu et al, 2016;Xu et al, 2017). In the present study, the complement test confirmed the recovery of abnormal morphology.…”

Balancing Strength and Flexibility: How the Synthesis, Organization, and Modification of Guard Cell Walls Govern Stomatal Development and Dynamics

“…Because de-methyl-esterified HG produced by PMEs can have contrasting mechanical effects on the wall depending on how the de-methyl-esterification occurs (Hocq et al, 2017 ), it is currently unknown how these PMEs alter the biomechanics of the guard cell wall. Because PMEs enzymatically remove methyl groups from the pectin backbone in the apoplast whereas putative PMTs are localized in the Golgi (Mouille et al, 2007 ; Kim et al, 2015 ; Xu et al, 2017 ; Figure 2 ), it is unlikely that a de-methylesterification/methylesterification cycle occurs on pectins in the apoplast during fast and reversible stomatal movements in mature guard cells. Instead, the de-methyl-esterification patterns of HG generated by PME activity and their mechanical effects on the guard cell wall are more likely established during guard cell morphogenesis (Movie S1 ).…”

Mutations in the Pectin Methyltransferase QUASIMODO2 Influence Cellulose Biosynthesis and Wall Integrity in Arabidopsis

“…Mutants for another allele of QUA2, osu1, are more sensitive to imbalanced C/N conditions, suggesting that QUA2 is also a key modulator of carbon and nitrogen nutrient balance during plant development (Gao et al, 2008). In addition, mutants of a rice (Oryza sativa) putative ortholog of AtQUA2 show altered wall composition and developmental defects (Qu et al, 2016;Xu et al, 2017). OsQUA2 shares high sequence similarity with AtQUA2, and mutation of OsQUA2 results in reduced HG methylesterification in culm-sieve element and root cell walls, affecting sucrose transport and root development, respectively (Qu et al, 2016;Xu et al, 2018).…”

“…In addition, mutants of a rice (Oryza sativa) putative ortholog of AtQUA2 show altered wall composition and developmental defects (Qu et al, 2016;Xu et al, 2017). OsQUA2 shares high sequence similarity with AtQUA2, and mutation of OsQUA2 results in reduced HG methylesterification in culm-sieve element and root cell walls, affecting sucrose transport and root development, respectively (Qu et al, 2016;Xu et al, 2018). QUASIMODO3 (QUA3), another putative HG methyltransferase, influences pectin methylesterification and regulates cell wall biosynthesis in Arabidopsis suspension-cultured cells (Miao et al, 2011).…”