Investigating the molecular basis for Rubisco acclimation to increasing temperature

假设：多亚基Rubisco酶的蛋白质同种型组成随环境温度的变化而变化。背景：核酮糖-1，5-二磷酸羧化酶-加氧酶（Rubisco）是地球上最丰富的酶，在无机CO2向有机碳化合物的光合转化中起着关键作用。这个复杂的过程是地球生命的基础，也是所有自然生态系统和人类食物链的基础。然而，与所有酶驱动的过程一样，CO2固定是一个温度敏感的过程，了解这一途径中的酶如何应对全球气温上升可能对农业（和藻类生物技术）产生重要影响。Rubisco是一种具有光合作用驱动羧化酶活性和破坏性加氧酶活性的双功能酶，本研究旨在通过对Rubisco复合物的特异性修饰来建立Rubisco适应高温的机制。后者以依赖于温度的方式降低光合效率，导致植物生产力降低。植物Rubisco具有由叶绿体基因rbcL编码的8个大亚基和由核rbcS基因家族编码的8个小亚基。叶绿体rbcL是一个单拷贝基因，它确保产生相同的大亚基蛋白。然而，核rbcS基因的多个拷贝产生不相同的小亚基蛋白。拟南芥rbcS基因的表达在一定温度范围内发生变化。此外，不同的中胚草rbcS基因在C3到CAM转换期间不成比例地下调。此外，菠菜Rubisco在不同温度下驯化后表现出不同的动力学特征。在不断变化的条件下，不同的rbcS表达谱和随之而来的Rubisco特性导致不同的rbcS基因编码的小亚基在微调Rubisco以适应不同的条件中发挥作用。这是加强了观察表明，植物暴露于季节性温度的显着变化，可能会改变其光合作用的最佳适应，以配合外部条件。该研究的目的是光合系统的温度敏感性/弹性的比较研究，特别侧重于Rubisco酶复合物在一系列模式生物和作物。

HYPOTHESIS: Protein isoform composition of the multi-subunit Rubisco enzyme changes in response to environmental temperature. This opens the possibility that Rubisco engineering could be used to increase the geographical range of important crops and safeguard food security in the wake of global warming.BACKGROUND: Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), the most abundant enzyme on earth, has a key function in photosynthetic conversion of inorganic CO2 into organic carbon compounds. This complex process is fundamental to life on earth and underpins all natural ecosystems and the human food chain. However, like all enzyme-driven processes, CO2 fixation is a temperature-sensitive process and an understanding of how enzymes in this pathway respond to rising global temperatures could have important implications in agriculture (and algal biotechnology). This project aims to establish the mechanism by which Rubisco acclimates to high temperatures through specific modifications to the enzyme complex.Rubisco is a bifunctional enzyme with photosynthesis-driving carboxylase activity and the subversive oxygenase activity. The latter decreases photosynthetic efficiency in a temperature-dependent fashion, leading to reduced plant productivity. Plant Rubisco has eight large subunits encoded by the chloroplast gene rbcL and eight small subunits encoded by a family of nuclear rbcS genes. The chloroplast rbcL is a single-copy gene, which ensures production of identical large-subunit proteins. However, multiple copies of nuclear rbcS genes produce nonidentical small-subunit proteins. Expression of Arabidopsis rbcS genes changes under a range of temperatures. Additionally, different Mesembryanthemum crystallinum rbcS genes are disproportionately down-regulated during C3 to CAM switch. Furthermore, rubisco of Spinacia oleracea displays different kinetic profiles after acclimation at different temperatures. Different rbcS expression profiles and attendant Rubisco properties in plants under changing conditions led to the proposal that different rbcS gene-encoded small subunits have a role in fine-tuning Rubisco to acclimate to different conditions. This is reinforced by observations suggesting that plants exposed to significant changes in seasonal temperature may acclimate by shifting their photosynthetic optimum to match the external conditions. The study objective is a comparative study of the temperature sensitivity/resilience of photosynthetic systems, with particular focus on the Rubisco enzyme complex in a range of model organisms and crops.