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Transcription Factors BLH2 and BLH4 Regulate Demethylesterification of Homogalacturonan in Seed Mucilage.
Plant Physiology ( IF 6.5 ) Pub Date : 2020-02-28 , DOI: 10.1104/pp.20.00011 Yan Xu 1 , Yiping Wang 1 , Xiaoyu Wang 1 , Shengqiang Pei 1 , Yingzhen Kong 2 , Ruibo Hu 1 , Gongke Zhou 2, 3
Plant Physiology ( IF 6.5 ) Pub Date : 2020-02-28 , DOI: 10.1104/pp.20.00011 Yan Xu 1 , Yiping Wang 1 , Xiaoyu Wang 1 , Shengqiang Pei 1 , Yingzhen Kong 2 , Ruibo Hu 1 , Gongke Zhou 2, 3
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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. BLH2 and BLH4 were significantly expressed in mucilage secretory cells during seed mucilage production. BLH2 and BLH4 single mutants exhibited no obvious mucilage phenotype, but the blh2 blh4 double mutant displayed significantly reduced mucilage adherence to the seed. Reduced mucilage adherence in blh2 blh4 was 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, including PME58, PECTIN METHYLESTERASE INHIBITOR6, SEEDSTICK, and MYB52 was significantly altered in blh2 blh4 seeds. BLH2 and BLH4 directly activated PME58 expression by binding to its TGACAGGT cis-element. Moreover, pme58 mutants exhibited reduced mucilage adherence similar to that of blh2 blh4, and the blh2 blh4 pme58 triple mutant exhibited no additional mucilage adherence defects. Furthermore, overexpression of PME58 in blh2 blh4 rescued the mucilage adherence defect. Together, these results demonstrate that BLH2 and BLH4 redundantly regulate de-methylesterification of HG in seed mucilage by directly activating PME58.
中文翻译：
转录因子BLH2和BLH4调节种子黏液中同型半乳糖醛酸的去甲基酯化。
多糖果胶是植物细胞壁的主要成分。果胶聚糖同半乳糖醛酸聚糖（HG）是专门的种子细胞壁（称为粘液）的比例较小但重要的组成部分。HG以高度甲基酯化的形式合成，并在分泌后被果胶甲基酯酶（PME）脱甲基酯化。HG的甲基酯化程度决定了果胶的结构和功能特性，但是如何调节甲基酯化仍然很大程度上未知。在这里，我们确定了两个BEL1-Like同源域（BLH）转录因子BLH2和BLH4，作为拟南芥（Arabidopsis thaliana）种皮粘液中HG脱甲基酯化的正向调节剂。在种子粘液产生过程中，BLH2和BLH4在粘液分泌细胞中表达明显。BLH2和BLH4单突变体没有明显的粘液表型，但是blh2 blh4双突变体显示出粘液对种子的依从性明显降低。blh2 blh4黏液黏附力的降低是由于种皮中PME活性降低，从而增加了黏液中HG的甲基化程度。在blh2 blh4种子中，包括PME58，果胶甲基酶抑制剂6，SEEDSTICK和MYB52在内的几种PME代谢相关基因的表达发生了显着变化。BLH2和BLH4通过与其TGACAGGT顺式元件结合直接激活PME58表达。此外，pme58突变体表现出与blh2 blh4相似的降低的粘液粘附性，而blh2 blh4 pme58三重突变体没有显示出额外的粘液粘附缺陷。此外，PME58在blh2 blh4中的过表达挽救了粘液黏附缺陷。总之，这些结果表明，BLH2和BLH4通过直接激活PME58冗余地调节了种子粘液中HG的脱甲基酯化。
更新日期：2020-05-01
中文翻译：
转录因子BLH2和BLH4调节种子黏液中同型半乳糖醛酸的去甲基酯化。
多糖果胶是植物细胞壁的主要成分。果胶聚糖同半乳糖醛酸聚糖（HG）是专门的种子细胞壁（称为粘液）的比例较小但重要的组成部分。HG以高度甲基酯化的形式合成，并在分泌后被果胶甲基酯酶（PME）脱甲基酯化。HG的甲基酯化程度决定了果胶的结构和功能特性，但是如何调节甲基酯化仍然很大程度上未知。在这里，我们确定了两个BEL1-Like同源域（BLH）转录因子BLH2和BLH4，作为拟南芥（Arabidopsis thaliana）种皮粘液中HG脱甲基酯化的正向调节剂。在种子粘液产生过程中，BLH2和BLH4在粘液分泌细胞中表达明显。BLH2和BLH4单突变体没有明显的粘液表型，但是blh2 blh4双突变体显示出粘液对种子的依从性明显降低。blh2 blh4黏液黏附力的降低是由于种皮中PME活性降低，从而增加了黏液中HG的甲基化程度。在blh2 blh4种子中，包括PME58，果胶甲基酶抑制剂6，SEEDSTICK和MYB52在内的几种PME代谢相关基因的表达发生了显着变化。BLH2和BLH4通过与其TGACAGGT顺式元件结合直接激活PME58表达。此外，pme58突变体表现出与blh2 blh4相似的降低的粘液粘附性，而blh2 blh4 pme58三重突变体没有显示出额外的粘液粘附缺陷。此外，PME58在blh2 blh4中的过表达挽救了粘液黏附缺陷。总之，这些结果表明，BLH2和BLH4通过直接激活PME58冗余地调节了种子粘液中HG的脱甲基酯化。
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