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A ligand-independent origin of abscisic acid perception
First author: Yufei Sun; Affiliations: The Hebrew University of Jerusalem (耶路撒冷希伯來大學): Rehovot, Israel
Corresponding author: Assaf Mosquna
Land plants are considered monophyletic, descending from a single successful colonization of land by an aquatic algal ancestor. The ability to survive dehydration to the point of desiccation is a key adaptive trait enabling terrestrialization. In extant land plants, desiccation tolerance depends on the action of the hormone abscisic acid (ABA) that acts through a receptor-signal transduction pathway comprising a PYRABACTIN RESISTANCE 1-like (PYL)–PROTEIN PHOSPHATASE 2C (PP2C)–SNF1-RELATED PROTEIN KINASE 2 (SnRK2) module. Early-diverging aeroterrestrial algae mount a dehydration response that is similar to that of land plants, but that does not depend on ABA: Although ABA synthesis is widespread among algal species, ABA-dependent responses are not detected, and algae lack an ABA-binding PYL homolog. This raises the key question of how ABA signaling arose in the earliest land plants. Here, we systematically characterized ABA receptor-like proteins from major land plant lineages, including a protein found in the algal sister lineage of land plants. We found that the algal PYL-homolog encoded by Zygnema circumcarinatum has basal, ligand-independent activity of PP2C repression, suggesting this to be an ancestral function. Similarly, a liverwort receptor possesses basal activity, but it is further activated by ABA. We propose that co-option of ABA to control a preexisting PP2C-SnRK2-dependent desiccation-tolerance pathway enabled transition from an all-or-nothing survival strategy to a hormone-modulated, competitive strategy by enabling continued growth of anatomically diversifying vascular plants in dehydrative conditions, enabling them to exploit their new environment more efficiently.
陸地植物被認為是單系起源，源自於單個成功殖民陸地的水生藻類植物祖先。能夠在某個特定乾燥點下脫水生存是陸地化成功的一個關鍵適應性性狀。在現存的陸地植物中，脫水耐受性依賴於植物激素脫落酸ABA介導的一個受體信號轉導通路，包含著一個PYL-PP2C-SnRK2模塊。早期分化出來的綠藻具有類似於陸地植物的脫水響應，但並不依賴於ABA；儘管ABA合成在藻類植物中廣泛存在，但並未檢測到ABA依賴性的響應，並且綠藻缺少一個ABA結合PYL同源物。這引出了一個關鍵的問題，即ABA信號轉導如何在早期陸地植物中出現的。本文中，作者系統性研究了主要陸地植物支系的ABA類受體蛋白，包括一個在陸地植物的藻類姊妹支中發現的蛋白。作者發現藻類Zygnema circumcarinatum中PYL同源物具有基礎的、獨立於配體的PP2C抑制活性，說明這可能是一個古老的功能。同樣，一個地錢受體擁有基礎的活性，但其會被ABA進一步激活。作者假設通過對ABA的共選擇來控制一個預先存在的PP2C-SnRK2依賴性脫水耐受性通路，從全有或全無的生存策略過渡到激素調節的競爭策略，該過程主要是通過使得結構上多樣化的維管植物在乾燥條件下持續性的生長，使其能夠更加有效地開發他們新的生存環境。
通訊：Assaf Mosquna (https://plantscience.agri.huji.ac.il/assafmosquna)
研究方向：植物對環境脅迫的響應；植物中的ABA信號轉導通路和相關的細胞、生理脅迫響應。
doi: https://doi.org/10.1073/pnas.1914480116
Journal: PNAS
First Published: November 19, 2019