Evolutionarily Conserved Regulatory Mechanisms of Abscisic Acid Signaling in Land Plants: Characterization of ABSCISIC ACID INSENSITIVE1-Like Type 2C Protein Phosphatase in the Liverwort Marchantia polymorpha
Evolutionarily Conserved Regulatory Mechanisms of Abscisic Acid Signaling in Land Plants: Characterization of ABSCISIC ACID INSENSITIVE1-Like Type 2C Protein Phosphatase in the Liverwort Marchantia polymorpha
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DOI：
10.1104/pp.110.153387
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发表时间：
2010-03-01
期刊：
影响因子：
7.4
通讯作者：
Takezawa, Daisuke
中科院分区：
文献类型：
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作者：
Tougane, Ken;Komatsu, Kenji;Takezawa, Daisuke
脱落酸（阿坝）被认为是一种普遍存在的激素，在维管植物种子发育和对环境胁迫的反应中起着重要作用。然而，在地钱（地钱门），这是最古老的现存谱系的陆地植物中，阿坝的作用一直强调最少，因此，很少有信息是阿坝反应的分子机制。在这项研究中，我们分离和表征MPABI 1，脱落酸不敏感1（ABI 1）的直系同源物，地钱多形。MpABI 1 cDNA编码一个568个氨基酸的蛋白质，由羧基端蛋白磷酸酶2C（PP 2C）结构域和一个新的氨基端调节结构域组成。在配子体中检测到MpABI 1的转录本，外源阿坝处理可提高其在芽中的表达水平，而芽的生长受到阿坝的强烈抑制。利用绿色荧光蛋白融合构建体的实验表明，MpABI 1主要定位于细胞核，其核定位是由氨基末端结构域。MpABI 1在M. polymorpha和小立碗藓细胞导致ABA诱导的与β-葡萄糖醛酸酶基因融合的小麦Em启动子表达的抑制。表达MpABI 1的转基因小球藻及其缺失氨基端结构域的突变体MpABI 1-d2具有降低的冷冻和渗透胁迫耐受性，并且与ABA诱导的胚胎发育后期丰富样煮沸可溶性蛋白的积累减少相关。此外，ABA诱导的形态变化，导致育雏细胞在这些转基因植物中并不突出。这些结果表明，MPABI 1是阿坝信号的负调节，提供了明确的分子证据PP 2C介导的阿坝反应机制在苔类植物中发挥作用。
Abscisic acid (ABA) is postulated to be a ubiquitous hormone that plays a central role in seed development and responses to environmental stresses of vascular plants. However, in liverworts (Marchantiophyta), which represent the oldest extant lineage of land plants, the role of ABA has been least emphasized; thus, very little information is available on the molecular mechanisms underlying ABA responses. In this study, we isolated and characterized MpABI1, an ortholog of ABSCISIC ACID INSENSITIVE1 (ABI1), from the liverwort Marchantia polymorpha. The MpABI1 cDNA encoded a 568-amino acid protein consisting of the carboxy-terminal protein phosphatase 2C (PP2C) domain and a novel amino-terminal regulatory domain. The MpABI1 transcript was detected in the gametophyte, and its expression level was increased by exogenous ABA treatment in the gemma, whose growth was strongly inhibited by ABA. Experiments using green fluorescent protein fusion constructs indicated that MpABI1 was mainly localized in the nucleus and that its nuclear localization was directed by the aminoterminal domain. Transient overexpression of MpABI1 in M. polymorpha and Physcomitrella patens cells resulted in suppression of ABA-induced expression of the wheat Em promoter fused to the beta-glucuronidase gene. Transgenic P. patens expressing MpABI1 and its mutant construct, MpABI1-d2, lacking the amino-terminal domain, had reduced freezing and osmotic stress tolerance, and associated with reduced accumulation of ABA-induced late embryogenesis abundant-like boiling-soluble proteins. Furthermore, ABA-induced morphological changes leading to brood cells were not prominent in these transgenic plants. These results suggest that MpABI1 is a negative regulator of ABA signaling, providing unequivocal molecular evidence of PP2C-mediated ABA response mechanisms functioning in liverworts.