NSF Postdoctoral Fellowship in Biology FY 2019: Improving C4 Crop Tolerance for Heat Stress by Engineering Thermostable Rubisco Activase

这项行动为2019财年的NSF国家植物基因组计划生物学博士后研究奖学金提供资金。该研究金支持研究员在东道实验室的研究和培训计划，研究员还提出了扩大生物学参与的计划。莎拉·斯坦布鲁克（Sarah Stainbrook）奖学金的研究和培训计划的标题是“通过工程改造热稳定Rubisco活化酶提高C4作物对热应激的耐受性”。该奖学金的主办机构是唐纳德·丹福思植物科学中心（DDPSC），赞助科学家是张茹博士。全球人口增长，再加上向依赖生物燃料的过渡，将要求到2050年玉米和其他粮食作物的产量翻一番。然而，预计到2050年气温将上升3.5摄氏度，全球玉米产量将减少23%。即使是现在，美国在1980年、1988年和2012年经历的热浪也可能影响农业生产力，损失估计分别为550亿美元、710亿美元和310亿美元。解决这一迫在眉睫的粮食安全危机的一个办法是通过提高作物的耐热性，以承受热应力，重点是Rubisco活化酶（Rca），光合作用中最敏感的酶。该项目将利用不同植物中Rca的天然变异，寻找或创造一种Rca酶变体，以提高玉米耐高温的能力。更广泛的影响包括教授非专业本科生物课，以提高科学素养，并通过DDPSC的突变小米外展计划指导来自贫困或少数民族背景的高中生。C3，C4和CAM是植物用于固定碳的三种不同的光合作用过程。在热胁迫期间限制碳固定的主要因素之一是碳固定酶Rubisco的活化状态。Rubisco必须由其催化伴侣Rubisco活化酶（Rca）活化。据估计，如果能够找到或创造一种热稳定的Rca，玉米的净光合速率在40摄氏度下可以翻一番。本研究将集中于从C4作物玉米和高粱以及密切相关的模式草狗尾草中鉴定和分离变异Rca酶。从这些植物中分离出的Rca将通过体外碳同化测定来表征，并与从完整植物中提取的叶绿素荧光和气体交换测量相关联。将类似地测定来自这些植物以及来自各种环境的C3、C4和CAM植物的热适应分离物，以确定Rca耐热性中天然存在的变异范围。此外，蛋白质工程技术将用于改善Rca热稳定性。将具有改进特性的变体引入S viridis中以验证工程化的热稳定酶提高转基因植物中光合作用的耐热性。一旦得到验证，工程热稳定Rca将被引入玉米。该项目产生的所有表型和生物化学数据，包括来自不同气候的植物的数据，将被添加到现有的遗传信息中，这些信息保存在一个可公开访问的数据库中，并通过同行评审的出版物和会议报告进一步传播。保留字：该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This action funds an NSF National Plant Genome Initiative Postdoctoral Research Fellowship in Biology for FY 2019. The fellowship supports a research and training plan in a host laboratory for the Fellow who also presents a plan to broaden participation in biology. The title of the research and training plan for this fellowship to Sarah Stainbrook is "Improving C4 Crop Tolerance for Heat Stress by Engineering Thermostable Rubisco Activase". The host institution for the fellowship is the Donald Danforth Plant Science Center (DDPSC) and the sponsoring scientist is Dr. Ru Zhang.Global population growth, coupled with a transition to dependence on biofuels, will require a doubling of production of maize and other grain crops by 2050. However, the projected 3.5 degrees Celsius temperature increase in 2050 will reduce global maize production by 23%. Even now, heat waves such as those experienced by the U.S. in 1980, 1988 and 2012 could devastate agricultural productivity, with losses estimated at 55, 71, and 31 billion dollars, respectively. One solution to this impending food security crisis is by improving the thermotolerance of crops to withstand heat stress by focusing on Rubisco activase (Rca), the most thermosensitive enzyme involved in photosynthesis. This project will leverage naturally occurring variation in Rca in different plants to find or create a Rca enzyme variant that can improve the ability of maize to withstand high temperatures. Broader impacts include teaching a non-majors undergraduate biology class to improve science literacy and mentoring high school students from underprivileged or minority backgrounds through the Mutant Millets outreach program at the DDPSC.C3, C4, and CAM are three different photosynthetic processes that plants use to fix carbon. One of the primary factors limiting carbon fixation during heat stress is the activation state of the carbon fixation enzyme Rubisco. Rubisco must be activated by its catalytic chaperone, Rubisco activase (Rca). It is estimated that the net photosynthesis rate of maize could be doubled at 40 degrees Celsius if a thermostable Rca could be found or created. This research will focus on identifying and isolating variant Rca enzymes from C4 crops maize and sorghum, as well as the closely related model grass, Setaria viridis. Rca isolates from these plants will be characterized by in vitro carbon assimilation assays and correlated to chlorophyll fluorescence and gas exchange measurements taken from intact plants. Heat-adapted isolates from these plants, as well as from C3, C4 and CAM plants from a variety of environments, will be similarly assayed to determine the range of naturally occurring variation in Rca thermotolerance. Additionally, protein engineering techniques will be used to improve Rca thermostability. Variants with improved properties will be introduced into S viridis to verify that the engineered thermostable enzyme improves thermotolerance of photosynthesis in the transgenic plant. Once verified, the engineered thermostable Rca will be introduced into maize. All phenotypic and biochemical data generated in this project, including from plants from diverse climates, will be added to existing genetic information maintained in a publicly accessible database and further disseminated through peer-reviewed publications and conference presentations. Keywords: thermotolerance, carbon fixation, maize, C4 photosynthesis, Rubisco activase.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.