Christopher D A, Mullet J E
Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843-2128.
Plant Physiol. 1994 Apr;104(4):1119-29. doi: 10.1104/pp.104.4.1119.
We studied the effects of spectral quality and fluence on the expression of several chloroplast-encoded photosynthesis genes and on the stability of their protein products in barley (Hordeum vulgare). During light-dependent chloroplast maturation, mRNA levels for psbD-psbC and psbA were maintained at higher levels compared with mRNAs encoding proteins for other photosynthesis functions (atpB, rbcL). Maintenance of psbD-psbC mRNA levels was accounted for by differential activation of the psbD-psbC light-responsive promoter by high-irradiance blue light and, secondarily, ultraviolet A (UV-A) radiation. Promoter activation was fluence dependent and required continuous illumination for 2 h at threshold fluences of 1.3 (blue light), 7.5 (white light), or 10 (UV-A) mumol m-2 s-1. From immunoblot analysis experiments, we showed that the psbD-psbC gene products D2 and CP43 undergo light-mediated turnover similar to light-labile D1. Other photosynthesis proteins such as the beta subunit of ATP synthase and the large subunit of ribulose-1,5-bisphosphate carboxylase were relatively stable. In the absence of protein synthesis, D2 degradation paralleled the degradation of D1 (relative half-lives, 9.5-10 h). CP43 decay was about half of D2 and D1 decay. In contrast with activation of the light-responsive promoter, the fluence-dependent degradation of D1, D2, and CP43 required 50- to 100-fold higher fluences of photosynthetically active white, red, blue, or UV-A irradiation. We interpret the different fluence and wavelength requirements to indicate that separate photosensory systems regulate activation of psbD-psbC transcription and turnover of D1, D2, and CP43. We propose that a blue light/UV-A photosensory pathway activates the psbD-psbC light-responsive promoter, differentially maintaining the capacity of mature chloroplasts to synthesize D2 and CP43, which are damaged and turned over in illuminated plants.
我们研究了光谱质量和光通量对大麦（Hordeum vulgare）中几个叶绿体编码的光合作用基因表达及其蛋白质产物稳定性的影响。在依赖光的叶绿体成熟过程中，与编码其他光合作用功能蛋白（atpB、rbcL）的mRNA相比，psbD - psbC和psbA的mRNA水平维持在较高水平。psbD - psbC mRNA水平的维持是由于高光强蓝光以及其次的紫外A（UV - A）辐射对psbD - psbC光响应启动子的差异激活。启动子激活依赖于光通量，并且在阈值光通量为1.3（蓝光）、7.5（白光）或10（UV - A）μmol m⁻² s⁻¹时需要连续光照2小时。通过免疫印迹分析实验，我们表明psbD - psbC基因产物D2和CP43经历类似于光不稳定的D1的光介导周转。其他光合作用蛋白，如ATP合酶的β亚基和1,5 - 二磷酸核酮糖羧化酶的大亚基相对稳定。在没有蛋白质合成的情况下，D2的降解与D1的降解平行（相对半衰期，9.5 - 10小时）。CP43的衰变约为D2和D1衰变的一半。与光响应启动子的激活相反，D1、D2和CP43的光通量依赖性降解需要光合活性的白光、红光、蓝光或UV - A照射的光通量高50至100倍。我们解释不同的光通量和波长要求表明不同的光感受系统调节psbD - psbC转录的激活以及D1、D2和CP43的周转。我们提出蓝光/UV - A光感受途径激活psbD - psbC光响应启动子，差异地维持成熟叶绿体合成D2和CP43的能力，D2和CP43在光照植物中会受损并周转。
