Data from Arabidopsis Plants Expressing Only the Redox-Regulated Rca-α Isoform Have Constrained Photosynthesis and Plant Growth

Rubisco activase (Rca) facilitates the release of sugar‐phosphate inhibitors from the active sites of Rubisco and thereby plays a central role in initiating and sustaining Rubisco activation. In Arabidopsis, alternative splicing of a single Rca gene results in two Rca isoforms, Rca‐α and Rca‐β. Redox modulation of Rca‐α regulates the function of Rca‐α and Rca‐β acting together to control Rubisco activation. Although Arabidopsis Rca‐α alone less effectively activates Rubisco in vitro , it is not known how CO2 assimilation and plant growth are impacted. Here, we show that two independent transgenic Arabidopsis lines expressing Rca‐α in the absence of Rca‐β (“Rca‐α only” lines) grew more slowly in various light conditions, especially under low light or fluctuating light intensity, and in a short day photoperiod compared to wildtype. Photosynthetic induction was slower in the Rca‐α only lines, and they maintained a lower rate of CO2 assimilation during both photoperiod types. Our findings suggest Rca oligomers composed of Rca‐α only are less effective in initiating and sustaining the activation of Rubisco than when Rca‐β is also present. Currently there are no examples of any plant species that naturally express Rca‐α only but numerous examples of species expressing Rca‐β only. That Rca‐α exists in most plant species, including many C3 and C4 food and bioenergy crops, implies its presence is adaptive under some circumstances.

核酮糖-1,5-二磷酸羧化酶/加氧酶活化酶（Rubisco activase，简称Rca）可介导糖磷酸酯抑制剂从核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的活性位点解离，在启动并维持Rubisco活化的过程中发挥核心作用。在拟南芥中，单个Rca基因的可变剪接可产生两种Rca同工型，即Rca-α与Rca-β。Rca-α的氧化还原调控可调节Rca-α与Rca-β的协同功能，进而控制Rubisco的活化过程。尽管单独的拟南芥Rca-α在体外活化Rubisco的效率较低，但目前尚不清楚其对植物二氧化碳同化与生长发育的具体影响。本研究证实，两株独立的、在缺失Rca-β的情况下仅表达Rca-α的转基因拟南芥株系（以下简称"仅Rca-α株系"），在多种光照条件下（尤其在弱光、光照波动环境以及短日照光周期中）的生长速度均慢于野生型拟南芥。仅Rca-α株系的光合诱导过程更为迟缓，且在两种光周期下均维持更低的二氧化碳同化速率。本研究结果表明，仅由Rca-α构成的Rca寡聚体，在启动并维持Rubisco活化方面的效率显著低于同时含有Rca-β的Rca寡聚体。目前尚未发现天然仅表达Rca-α的植物物种，但存在大量仅表达Rca-β的植物物种实例。Rca-α广泛存在于多数植物物种中，包括诸多C3、C4粮食作物与生物能源作物，这暗示其在特定环境条件下具有适应性优势。