[植物演化] 離層酸ABA受器的來源。20191128 PNAS

Plasmodesmata
Nov 28, 2019
3 min read

A ligand-independent origin of abscisic acid perception

Yufei Sun, Ben Harpazi, Akila Wijerathna-Yapa, Ebe Merilo, Jan de Vries, Daphna Michaeli, Maayan Gal, Andrew C. Cuming, Hannes Kollist, and Assaf Mosquna

Abstract

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 hormonemodulated, competitive strategy by enabling continued growth of anatomically diversifying vascular plants in dehydrative conditions, enabling them to exploit their new environment more efficiently.

離層酸受器的緣起與配位基並無直接關聯

摘要

陸生植物被認為是從一個水生藻類祖先，成功登陸到陸地的原始物種所演化而來的單系群。能夠順利的在陸地上生活，其中一個重要演化出的能力是可以適應並存活在缺水的狀況下。在多數的陸生植物中，對於缺水的耐受度都仰賴於離層酸ABA的功能，這個荷爾蒙的調控路經是由PYL-PP2C-SnRK2這個模組所組成。早期分化出來可存活於溼地上的藻類，具備著與陸生植物相似、抵抗缺水狀態的反應，但是這個反應並不依靠離層酸。雖然離層酸的生合成廣泛的存在在很多的藻類中，但是藻類卻缺乏離曾酸所引起的反應。並且，藻類還缺少了可以結合離層酸的PYL同源基因。這引發了一個重要的問題：離層酸的訊息傳遞是如何在陸生植物中演化出來的呢？在此，我們系統性地從主要的陸生植物系中，鑑定了類似離層酸受器的蛋白質，其中包含了一個在陸生植物的姐妹系藻類中，發現的一個蛋白質。我們發現藻類Zygnema circumcarinatum的PYL同源基因編碼了具有基礎的、獨立於配位基的PP2C抑制功能。顯示出這個功能可能是一個原始的功能。相似的情況下，在苔類的受器也有基礎的活性，但是可以被離層酸進一步的活化。我們提出了離層酸可以共同作用，來調控一個早先就演化出來、依靠PP2C-SnRK2作用的耐缺水的訊息傳導路徑。這個共同作用，使得原來是全有全無的求生策略轉化成一個經由荷爾蒙所調節的競爭策略，讓在構造上相異的維管束植物，可以在缺水的狀態下繼續生長，使他們可以更有效地探索新的環境。