Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA.
Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat, Assam 785013, India.
Plant Cell Physiol. 2021 Mar 25;62(1):125-142. doi: 10.1093/pcp/pcaa146.
The plastidial starch phosphorylase (Pho1) functions in starch metabolism. A distinctive structural feature of the higher Pho1 is a 50-82-amino-acid long peptide (L50-L82), which is absent in phosphorylases from non-plant organisms. To study the function of the rice Pho1 L80 peptide, we complemented a pho1- rice mutant (BMF136) with the wild-type Pho1 gene or with a Pho1 gene lacking the L80 region (Pho1ΔL80). While expression of Pho1 in BMF136 restored normal wild-type phenotype, the introduction of Pho1ΔL80 enhanced the growth rate and plant productivity above wild-type levels. Mass spectrometry analysis of proteins captured by anti-Pho1 showed the surprising presence of PsaC, the terminal electron acceptor/donor subunit of photosystem I (PSI). This unexpected interaction was substantiated by reciprocal immobilized protein pull-down assays of seedling extracts and supported by the presence of Pho1 on isolated PSI complexes resolved by blue-native gels. Spectrophotometric studies showed that Pho1ΔL80 plants exhibited modified PSI and enhanced CO2 assimilation properties. Collectively, these findings indicate that the higher plant Pho1 has dual roles as a potential modulator of source and sink processes.
质体淀粉磷酸化酶（Pho1）在淀粉代谢中发挥作用。高等 Pho1 的一个显著结构特征是一个 50-82 个氨基酸长的肽（L50-L82），它不存在于非植物生物的磷酸化酶中。为了研究水稻 Pho1 L80 肽的功能，我们用野生型 Pho1 基因或缺失 L80 区域的 Pho1 基因（Pho1ΔL80）来补充 pho1-水稻突变体（BMF136）。虽然 Pho1 在 BMF136 中的表达恢复了正常的野生型表型，但引入 Pho1ΔL80 增强了生长速度和植物生产力，超过了野生型水平。通过抗 Pho1 捕获的蛋白质的质谱分析，出人意料地发现了 PsaC，即光系统 I（PSI）的末端电子受体/供体亚基。这种意想不到的相互作用通过幼苗提取物的互锁固定蛋白下拉测定得到证实，并得到了 Pho1 存在于通过蓝色-native 凝胶分离的分离 PSI 复合物上的支持。分光光度研究表明，Pho1ΔL80 植物表现出修饰的 PSI 和增强的 CO2 同化特性。总的来说，这些发现表明高等植物 Pho1 具有作为源和汇过程潜在调节剂的双重作用。
