Arsovski Andrej A, Villota Maria M, Rowland Owen, Subramaniam Rajagopal, Western Tamara L
Department of Biology, McGill University, Montreal, QC, Canada H3A 1B1.
J Exp Bot. 2009;60(9):2601-12. doi: 10.1093/jxb/erp102. Epub 2009 Apr 28.
Pollination triggers not only embryo development but also the differentiation of the ovule integuments to form a specialized seed coat. The mucilage secretory cells of the Arabidopsis thaliana seed coat undergo a complex differentiation process in which cell growth is followed by the synthesis and secretion of pectinaceous mucilage. A number of genes have been identified affecting mucilage secretory cell differentiation, including MUCILAGE-MODIFIED4 (MUM4). mum4 mutants produce a reduced amount of mucilage and cloning of MUM4 revealed that it encodes a UDP-L-rhamnose synthase that is developmentally up-regulated to provide rhamnose for mucilage pectin synthesis. To identify additional genes acting in mucilage synthesis and secretion, a screen for enhancers of the mum4 phenotype was performed. Eight mum enhancers (men) have been identified, two of which result from defects in known mucilage secretory cell genes (MUM2 and MYB61). Our results show that, in a mum4 background, mutations in MEN1, MEN4, and MEN5 lead to further reductions in mucilage compared to mum4 single mutants, suggesting that they are involved in mucilage synthesis or secretion. Conversely, mutations in MEN2 and MEN6 appear to affect mucilage release rather than quantity. With the exception of men4, whose single mutant exhibits reduced mucilage, none of these genes have a single mutant phenotype, suggesting that they would not have been identified outside the compromised mum4 background.
授粉不仅触发胚胎发育，还引发胚珠珠被分化以形成特化的种皮。拟南芥种皮的黏液分泌细胞经历复杂的分化过程，其中细胞生长之后是果胶类黏液的合成与分泌。已鉴定出许多影响黏液分泌细胞分化的基因，包括黏液修饰4（MUCILAGE-MODIFIED4，MUM4）。mum4突变体产生的黏液量减少，对MUM4的克隆显示它编码一种UDP-L-鼠李糖合酶，该酶在发育过程中上调，为黏液果胶合成提供鼠李糖。为了鉴定在黏液合成和分泌中起作用的其他基因，对mum4表型的增强子进行了筛选。已鉴定出8个mum增强子（men），其中两个是已知黏液分泌细胞基因（MUM2和MYB61）存在缺陷导致的。我们的结果表明，在mum4背景下，MEN1、MEN4和MEN5中的突变导致与mum4单突变体相比黏液进一步减少，这表明它们参与黏液合成或分泌。相反，MEN2和MEN6中的突变似乎影响黏液释放而非数量。除了men4单突变体表现出黏液减少外，这些基因均没有单一突变体表型，这表明在mum4受损背景之外它们不会被鉴定出来。
