Transcription Factors BLH2 and BLH4 Regulate Demethylesterification of Homogalacturonan in Seed Mucilage
Transcription Factors BLH2 and BLH4 Regulate Demethylesterification of Homogalacturonan in Seed Mucilage
复制标题
转录因子 BLH2 和 BLH4 调节种子粘液中同型半乳糖醛酸的去甲基酯化
DOI：
10.1104/pp.20.00011
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发表时间：
2020
期刊：
影响因子：
7.4
通讯作者：
Zhou Gongke
中科院分区：
文献类型：
--
作者：
Xu Yan;Wang Yiping;Wang Xiaoyu;Pei Shengqiang;Kong Yingzhen;Hu Ruibo;Zhou Gongke
多糖果胶是植物细胞壁的主要成分。果胶聚糖同型半乳糖醛酸（HG）是一个比例小，但重要的组成部分，一个专门的种子细胞壁称为粘液。HG以高度甲基化的形式合成，并且在分泌之后，通过果胶甲基酯酶（PME）脱甲基化。HG的甲酯化程度决定了果胶的结构和功能性质，但甲酯化如何调节仍然是一个未知数。在此，我们鉴定了两个BEL1样同源结构域（BLH）转录因子BLH2和BLH4，作为拟南芥中HG去甲酯化的正调控因子结果表明，BLH 2和BLH 4在种子粘液分泌细胞中表达显著，单突变体没有表现出明显的粘液表型，而双突变体blh 2和blh 4的粘液粘附能力显著降低。blh2 blh4的粘液粘附性降低是由于种皮中PME活性降低，从而增加了粘液中HG的甲酯化程度。在blh 2 blh 4种子中，PME 58、果胶甲基酯酶抑制剂6、SEEDSTICK和MYB 52等几个PME代谢相关基因的表达发生了显著变化。BLH2和BLH4通过与其TGACAGGT顺式元件结合直接激活PME58的表达。此外，pme 58突变体表现出减少的粘液粘附类似于blh 2 blh 4，和blh 2 blh 4 pme 58三重突变体没有表现出额外的粘液粘附缺陷。此外，在blh 2 blh 4中PME58的过表达挽救了粘液粘附缺陷。总之，这些结果表明BLH2和BLH4通过直接激活PME58冗余地调节种子粘液中HG的去甲酯化。
The polysaccharide pectin is a major component of the plant cell wall. The pectic glycan homogalacturonan (HG) is a proportionally small but important component of a specialized seed cell wall called mucilage. HG is synthesized in a highly methylesterified form, and, following secretion, is de-methylesterified by pectin methylesterases (PMEs). The degree of methylesterification of HG determines the structural and functional properties of pectin, but how methylesterification is regulated remains largely unknown. Here, we identified two BEL1-Like homeodomain (BLH) transcription factors, BLH2 and BLH4, as positive regulators of HG de-methylesterification in Arabidopsis (Arabidopsis thaliana) seed coat mucilage.BLH2andBLH4were significantly expressed in mucilage secretory cells during seed mucilage production.BLH2andBLH4single mutants exhibited no obvious mucilage phenotype, but theblh2 blh4double mutant displayed significantly reduced mucilage adherence to the seed. Reduced mucilage adherence inblh2 blh4was caused by decreased PME activity in the seed coat, which increased the degree of methylesterification of HG in mucilage. The expression of several PME metabolism-related genes, includingPME58,PECTIN METHYLESTERASE INHIBITOR6,SEEDSTICK, andMYB52was significantly altered inblh2 blh4seeds. BLH2 and BLH4 directly activatedPME58expression by binding to its TGACAGGT cis-element. Moreover,pme58mutants exhibited reduced mucilage adherence similar to that ofblh2 blh4, and theblh2 blh4 pme58triple mutant exhibited no additional mucilage adherence defects. Furthermore, overexpression ofPME58inblh2 blh4rescued the mucilage adherence defect. Together, these results demonstrate that BLH2 and BLH4 redundantly regulate de-methylesterification of HG in seed mucilage by directly activatingPME58.