Photoprotection in Diverse, Desiccation-Tolerant, Desert Green Algae and Their Close Aquatic Relatives

本研究的目的是确定沙漠绿色藻类在脱水和复水过程中保护光合机构的机制。 地球生命进化的关键一步是从生活在水中到陆地上生存。实现这一飞跃的生物体面临着强光、极端温度和干燥。开花植物、针叶树、苔藓和蕨类植物都是从一个成功入侵陆地的绿色藻类祖先进化而来的。它们共有的特征可能是在陆地上生存所必需的，或者它们可能只是从共同祖先那里继承来的特征。 为了区分这两种可能性，必须研究其他绿色光合作用的陆生生物，它们不是从共同的绿色藻类祖先传下来的。这种生物体存在于美国西南部沙漠的微生物结皮中的多种自由生活的微观绿色藻类中。沙漠绿色藻类比它们的水生藻类亲戚在干燥中存活得更好，并且沙漠藻类在再水合时非常迅速地（在几分钟内）从干燥中恢复。因此，它们是研究植物脱水耐性基本机制的理想体系。在干旱、高温和寒冷的情况下，陆地植物为了保护自己免受强烈阳光的伤害而发展的特性，随着农业向边缘土地扩展，而气候也发生了变化，这些特性变得尤为重要。沙漠绿色藻类与较大的农业和生态上重要的绿色植物以及越来越多地用于生物燃料生产的绿色藻类共享许多特征。 研究与教育和培训的整合将包括6- 8年级课程计划的开发，可供教师在科德角国家海岸带领游览重点是“令人惊讶的沙丘微生物”。 本科生的研究机会将集中在研究绿色植物和微生物结皮中的干燥胁迫和光生物学的项目上。总体研究目标是确定在四个藻类纲内的成对沙漠和水生绿色藻类中，在干燥和再水化过程中保护光合机构的快速可逆机制的过程（和系统发育分布）。 广泛的系统发育分布的光保护或耐干燥机制在沙漠成员的多个绿色藻类类将建议（通过简约），这些机制可能是祖先的性状在较大的绿色植物分支。在沙漠和密切相关的水生亲属的性状比较将确定谱系特异性特征。研究将确定耐干燥能力和干燥诱导的光保护能力是否具有持久的遗传成分（即使藻类是在水化条件下生长的），以及光和干燥速度对光保护效率的影响是否与它们对地衣和苔藓的影响相似。 最近已提出的机制，干燥诱导的光保护（PSII PSI溢出，P700+氧化，叶绿素-叶绿素电荷转移状态）将在地衣Parmelia sulcata和耐干燥绿色藻类荧光衰减动力学和建模，EPR，线性和圆二色光谱进行测试。 全转录组鸟枪测序将被用来测试是否，如在brabrites，转录组在代表性的沙漠衍生的绿色栅藻圆拥有constitive细胞保护干燥。

The objective of this research is to determine the process(es) underlying the mechanism(s) protecting the photosynthetic apparatus of desert green algae during desiccation and rehydration. A key step in the evolution of life on Earth was the move from living in water to surviving on land. Organisms making that leap faced high light levels, extreme temperatures, and desiccation. Flowering plants, conifers, mosses, and ferns are all descended from a single green algal ancestor that successfully invaded land. Traits they share may be essential for surviving on land, or they might simply be traits inherited from the common ancestor. To tease apart these two possibilities, other green, photosynthetic, terrestrial organisms must be studied that are not descended from that common green algal ancestor. Such organisms are found among diverse, free-living, microscopic green algae inhabiting microbiotic crusts of the desert Southwestern U.S. Desert green algae survive desiccation much better than their aquatic algal relatives, and desert algae recover from desiccation very rapidly (within minutes) when rehydrated. Thus, they make an ideal system to study basic mechanisms of desiccation tolerance. The traits land plants developed to protect themselves from intense sunlight during drought, high heat, and cold are particularly important as agriculture expands into marginal lands while climate also shifts. Desert green algae share many characteristics with larger agriculturally and ecologically important green plants, and also with the green algae increasingly used for biofuel production. Research integration with education and training will include development of 6-8th grade Lesson Plans, available to teachers leading excursions at Cape Cod National Seashore focusing on "Surprising Microbes of the Dunes". Research opportunities for undergraduates will be focused on projects studying desiccation stress and photobiology in green plants and microbiotic crusts.The overall research objective is to determine the process(es) underlying (and phylogenetic distribution of) rapidly-reversible mechanism(s) protecting the photosynthetic apparatus during desiccation and rehydration, in paired desert and aquatic green algae within four algal classes. Broad phylogenetic distribution of photoprotective or desiccation-tolerance mechanisms across desert members of multiple green algal classes will suggest (through parsimony) that these mechanisms are likely ancestral traits in the larger green plant clade. Comparison of traits in desert and closely-related aquatic relatives will identify lineage-specific characteristics. Research will establish whether the capacity for desiccation tolerance and desiccation-induced photoprotection has a persistent genetic component (even when algae are grown hydrated), and whether influences of light and speed of desiccation on the efficiency of photoprotection are similar to their effects in lichens and mosses. Mechanisms that have been recently proposed to underlie desiccation-induced photoprotection (PSII to PSI spillover, P700+ oxidation, and chlorophyll-chlorophyll charge transfer states) will be tested in the lichen Parmelia sulcata and desiccation-tolerant green algae using fluorescence decay kinetics and modeling, EPR, and linear and circular dichroism spectroscopy. Whole transcriptome shotgun sequencing will be used to test whether, as in bryophytes, the transcriptome in the representative desert-derived green alga Scenedesmus rotundus possesses constititive cellular protection against desiccation.