Carotology: Are apocarotenoids conserved modulators of streptophyte physiology?

对于最早的陆地植物来说，一个主要的挑战是克服环境压力。陆生植物的叶绿体被认为是感知环境信号的中枢，它通过发出信号，将叶绿体与细胞生理学联系起来。这些信号中的一大类是从类胡萝卜素裂解中产生的类胡萝卜素。在Madland的第一个资助期，我和我的团队已经获得了数据，陆地植物和链藻分享了一系列与胁迫相关的非胡萝卜素的产生，这些类胡萝卜素被称为胚芽植物中的信号。现在，我们想要了解这些分子会引发哪些生理和分子反应。我们将检验这样的假设，即类胡萝卜素β-cycLocitral、β-紫罗兰酮和二氢Acinidiolide诱导与胁迫信号相关的保守反应模式；对于所有的工作，我们将使用Madland系统的Mesotaum endlicherianum、Zygnema arcarinata和Physcomitrium patens作为陆地植物的参考。为了剖析对类阿帕胡萝卜素的响应，我们将追求三个协同目标：(1)测量类阿类胡萝卜素对合子植物和陆地植物生长、光生理学的影响，以及对上游异戊二烯代谢的反馈；我们将阐明陆地植物和藻类共享的阿类胡萝卜素的生理影响。(2)推断在6亿年的链柄植物进化过程中共有的由类阿类胡萝卜素触发的全球反应模式；整合RNAseq和磷酸蛋白质组数据将精确定位综合反应模式-信号转导到下游反应的候选-我们可以比较这些模式来推断共享的同源信号网络。(3)探索信号通路的保守性；虽然载脂类胡萝卜素的一系列作用将在自上而下的方法中进行评估，但我们也有明确的候选者：植物激素水杨酸和延伸的下胚轴5(HY5)和植物色素相互作用因子3(PIF3)的(共同)同源物。我们将通过(I)与已产生的Physcomitrium patens hy5和PIF基因敲除突变体中的藻类基因进行种间互补实验和(Ii)水杨酸定量来测试这些途径的保守性。总而言之，我们将获得关于类胡萝卜素生理影响的全面数据；同时，我们将使用自上而下和基于候选对象的有针对性的方法深入研究信号转导。我们的数据将被投射到芦苇藻类的系统发育上，并与已发表的陆地植物数据和链藻共表达数据进行比较。结合起来，我们将解决Madland(i-iv)的四个已定义的核心主题：(I)测试在链状藻类中进化的通过类胡萝卜素调节逆境生理的分子底盘；(Ii)推断这些调控模式发生在陆地植物和Zygnematophyceae的最后共同祖先中；(Iii)探讨它们作为分子适应在响应(Iv)非生物陆地挑战中的作用。

One major challenge for the earliest land plants was overcoming environmental stressors. The plastid of land plants is recognized as a hub for sensing environmental cues by emanating signals, linking plastid and cell physiology. A major class of these signals are the apocarotenoids that emerge from cleavage of carotenoids. In the first funding period of MAdLand, my team and I have garnered data that land plants and streptophyte algae share the production of a range of stress-relevant apocarotenoids known as signals in embryophytes. Now, we want to understand which physiological and molecular responses these molecules elicit. We will test the hypothesis that the apocarotenoids β-cyclocitral, β-ionone, and dihydroactinidiolide induce conserved response patterns tied with stress signaling; for all work, we will use the MAdLand systems Mesotaenium endlicherianum, Zygnema circumcarinatum, and Physcomitrium patens as a land plant reference. To dissect responses to apocarotenoids, we will pursue three synergistic objectives: (1) Measure the impact of apocarotenoids on zygnematophyte and land plant growth, photophysiology, and feedbacks on upstream isoprenoid metabolism; we will illuminate the physiological impact of apocarotenoids shared by land plants and algae. (2) Infer apocarotenoid-triggered global response patterns shared across 600 million years of streptophyte evolution; integrating RNAseq and phosphoproteomic data will pinpoint comprehensive response patterns—candidates for signal transduction to downstream responses—that we can compare to infer a shared homologous signaling network. (3) Probe the conservation of the signaling pathway; while a range of effects of apocarotenoids will be assessed in 1 and 2 in a top-down approach, we also have clear candidates: the phytohormone salicylic acid and (co-)orthologs of ELONGATED HYPOCOTYL 5 (HY5) and PHYTOCHROME INTERACTING FACTOR 3 (PIF3) in Mesotaenium, Zygnema, and Physcomitrium. We will test for the conservation of these routes via (i) inter-species complementation experiments with the algal genes in Physcomitrium patens hy5 and pif knock-out mutants that were already generated and (ii) salicylic acid quantification. In sum, we will obtain comprehensive data on the physiological impact of apocarotenoids; concomitantly, we will delve into signaling using a top-down and a targeted candidate-based approach. Our data will be projected onto the phylogeny of Phragmoplastophyta and compared to published data on land plants and co-expression data on streptophyte algae. Combined, we will address four defined core topics of MAdLand (i-iv): (i) testing that a molecular chassis for modulation of stress physiology through apocarotenoids evolved in streptophyte algae; (ii) inferring that these regulatory patterns occurred in the last common ancestor of land plants and Zygnematophyceae; (iii) probing their role as molecular adaptations in the response to (iv) abiotic terrestrial challenges.