Molecular evolution of starch degradation in the guard cells of CAM plants

CAM植物保卫细胞中淀粉降解的分子进化

• 批准号: 2132439
• 金额: --
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2132439
• 关键词: Molecular; evolution; starch; degradation; guard

The water conserving properties of CAM photosynthesis have identified the pathway as a target for synthetic biology. CAM conserves water by shifting net CO2 uptake to the night when rates of leaf evapotranspiration are reduced compared to the day. CAM improves water-use efficiency (CO2 fixed per unit water lost) some 5 to 10 fold over that in plants with other types of photosynthesis. Thus, bioengineering CAM into non-CAM crops offers the potential to sustain plant productivity for food, feed, fibre, and biofuel production whilst curtailing water inputs (Borland et al, 2014). The rationale for CAM-bioengineering is rooted in the knowledge that since CAM emerged frequently from C3 photosynthesis throughout evolutionary history, all of the enzymes required for CAM are homologues of ancestral forms found in C3 species. Thus, understanding the molecular evolution of key genes required for CAM is a crucial component for informing CAM engineering. Engineering CAM into C3 plants requires a day/night rescheduling of stomatal movement so that stomata (leaf pores) open at night and close during the day. Recent unpublished work in the Borland lab has suggested a fundamental difference in guard cell metabolism between CAM and C3 plants which merits further study. Specifically, starch breakdown in stomatal guard cells, which enhances guard cell turgor and accelerates day-time stomatal opening in C3 plants, is suppressed in CAM guard cells. Starch degradation in C3 guard cells requires a different enzymatic route to that in the leaf mesophyll and key enzymes required for C3 guard cell starch turnover have recently been identified in Arabidopsis. Our observations for CAM guard cells provide two hypotheses: 1) CAM guard cells lack key enzymes required for starch degradation; 2) Guard cell starch degradation is subject to contrasting modes of regulation in CAM and C3 plants. This project will test these hypotheses using a range of wet and dry lab approaches that include; a) analysis of the guard cell-enriched proteome of the model CAM plant Kalanchoë fedtschenkoi and how it compares to published guard cell proteomes of Arabidopsis, with particular focus on proteins implicated in starch and osmolyte turnover; b) genetic manipulation of selected candidate genes implicated in CAM guard cell starch metabolism and c) bioinformatics interrogation of published C3 and CAM genomes to establish molecular phylogenies of candidate genes implicated in guard cell starch degradation and to test if these genes have evolved differently in CAM and C3 plants.

CAM 光合作用的节水特性已将该途径确定为合成生物学的目标。 CAM 通过将 CO2 净吸收转移到夜间来节约用水，此时叶片蒸散量与白天相比有所降低。 CAM 提高了水分利用效率（单位水损失的二氧化碳固定量），比其他类型光合作用的植物提高了约 5 至 10 倍。因此，通过生物工程将 CAM 转化为非 CAM 作物，有可能维持植物的粮食、饲料、纤维和生物燃料生产生产力，同时减少水的投入（Borland 等，2014）。 CAM 生物工程的基本原理植根于这样的知识：由于在整个进化历史中 CAM 经常从 C3 光合作用中出现，因此 CAM 所需的所有酶都是 C3 物种中发现的祖先形式的同源物。因此，了解 CAM 所需关键基因的分子进化是了解 CAM 工程的重要组成部分。 将 CAM 工程化到 C3 植物中需要重新安排气孔运动的昼/夜时间，以便气孔（叶孔）在夜间打开并在白天关闭。 Borland 实验室最近未发表的工作表明 CAM 和 C3 植物之间的保卫细胞代谢存在根本差异，值得进一步研究。具体来说，气孔保卫细胞中的淀粉分解在 CAM 保卫细胞中受到抑制，淀粉分解可增强 C3 植物中保卫细胞的膨压并加速白天气孔的打开。 C3 保卫细胞中的淀粉降解需要与叶肉中不同的酶促途径，并且最近在拟南芥中鉴定了 C3 保卫细胞淀粉周转所需的关键酶。我们对 CAM 保卫细胞的观察提供了两个假设：1）CAM 保卫细胞缺乏淀粉降解所需的关键酶； 2) CAM 和 C3 植物中保卫细胞淀粉降解受到不同的调节模式的影响。该项目将使用一系列湿式和干式实验室方法来测试这些假设，包括： a) 分析 CAM 模型植物 Kalanchoë fedtschenkoi 的保卫细胞富集蛋白质组，以及如何将其与已发表的拟南芥保卫细胞蛋白质组进行比较，特别关注与淀粉和渗透剂周转有关的蛋白质； b) 对与 CAM 保卫细胞淀粉代谢有关的选定候选基因进行遗传操作，以及 c) 对已发表的 C3 和 CAM 基因组进行生物信息学分析，以建立与保卫细胞淀粉降解有关的候选基因的分子系统发育，并测试这些基因在 CAM 和 C3 植物中是否有不同的进化。