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Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya, 464-8602, Japan.
Institute for Glyco-core Research (iGCORE), Nagoya University, Chikusa, Nagoya, 464-8601, Japan.
Plant J. 2023 Feb;113(3):493-503. doi: 10.1111/tpj.16061. Epub 2022 Dec 29.
Arabinogalactan proteins (AGPs) are a plant-specific family of extracellular proteoglycans characterized by large and complex galactose-rich polysaccharide chains. Functional elucidation of AGPs, however, has been hindered by the high degree of redundancy of AGP genes. To uncover as yet unexplored roles of AGPs in Arabidopsis, a mutant of Hyp O-galactosyltransferase (HPGT), a critical enzyme that catalyzes the common initial step of Hyp-linked arabinogalactan chain biosynthesis, was used. Here we show, using the hpgt1,2,3 triple mutant, that a reduction in functional AGPs leads to a stomatal patterning defect in which two or more stomata are clustered together. This defect is attributed to increased and dysregulated symplastic transport following changes in plasmodesmata structure, such that highly permeable complex branched plasmodesmata with cavities in branching parts increased in the mutant. We also found that the hpgt1,2,3 mutation causes a reduction of cellulose in the cell wall and accumulation of pectin, which controls cell wall porosity. Our results highlight the importance of AGPs in the correct biogenesis of plasmodesmata, possibly acting through the regulation of cell wall properties surrounding the plasmodesmata.
阿拉伯半乳聚糖蛋白（AGPs）是植物特有的一类细胞外蛋白聚糖，其特征在于具有大而复杂的富含半乳糖的多糖链。然而，AGP基因的高度冗余阻碍了对AGPs功能的阐明。为了揭示AGPs在拟南芥中尚未被探索的作用，我们使用了Hyp O-半乳糖基转移酶（HPGT）的突变体，HPGT是一种催化Hyp连接的阿拉伯半乳聚糖链生物合成共同起始步骤的关键酶。在这里，我们使用hpgt1,2,3三重突变体表明，功能性AGPs的减少会导致气孔模式缺陷，即两个或更多气孔聚集在一起。这种缺陷归因于胞间连丝结构改变后共质体运输增加和失调，使得突变体中分支部分带有腔的高渗透性复杂分支胞间连丝增加。我们还发现，hpgt1,2,3突变导致细胞壁中纤维素减少和果胶积累，而果胶控制细胞壁孔隙率。我们的结果突出了AGPs在胞间连丝正确生物发生中的重要性，可能是通过调节胞间连丝周围的细胞壁特性来实现的。
