Im Chung-Soon, Eberhard Stephan, Huang Kaiyao, Beck Christoph F, Grossman Arthur R
Department of Plant Biology, Carnegie Institution, Stanford, CA 94306, USA.
Plant J. 2006 Oct;48(1):1-16. doi: 10.1111/j.1365-313X.2006.02852.x.
Phototropin (PHOT) is a photoreceptor involved in a variety of blue-light-elicited physiological processes including phototropism, chloroplast movement and stomatal opening in plants. The work presented here tests whether PHOT is involved in expression of light-regulated genes in Chlamydomonas reinhardtii. When C. reinhardtii was transferred from the dark to very low-fluence rate white light, there was a substantial increase in the level of transcripts encoding glutamate-1-semialdehyde aminotransferase (GSAT), phytoene desaturase (PDS) and light-harvesting polypeptides (e.g. LHCBM6). Increased levels of these transcripts were also elicited by low-intensity blue light, and this blue-light stimulation was suppressed in three different RNAi strains that synthesize low levels of PHOT. The levels of GSAT and LHCBM6 transcripts also increased following exposure of algal cells to low-intensity red light (RL). The red-light-dependent increase in transcript abundance was not affected by the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, implying that the influence of RL on transcript accumulation was not controlled by cytoplasmic redox conditions, and that a red-light photoreceptor(s) may be involved in regulating the levels of transcripts from specific photosynthesis-related genes in C. reinhardtii. Interestingly, elevated GSAT and LHCBM6 transcript levels in RL were significantly reduced in the PHOT RNAi strains, which raises the possibility of co-action between blue and RL signaling pathways. Microarray experiments indicated that the levels of several transcripts for photosystem (PS) I and II polypeptides were also modulated by PHOT. These data suggest that, in C. reinhardtii, (i) PHOT is involved in blue-light-mediated changes in transcript accumulation, (ii) synchronization of the synthesis of chlorophylls (Chl), carotenoids, Chl-binding proteins and other components of the photosynthetic apparatus is achieved, at least in part, through PHOT-mediated signaling, and (iii) a red-light photoreceptor can also influence levels of certain transcripts associated with photosynthetic function, although its action requires normal levels of PHOT.
向光素（PHOT）是一种光感受器，参与多种蓝光诱导的生理过程，包括植物的向光性、叶绿体运动和气孔开放。本文的研究旨在测试PHOT是否参与莱茵衣藻中光调节基因的表达。当莱茵衣藻从黑暗转移到极低光通量率的白光下时，编码谷氨酸-1-半醛转氨酶（GSAT）、八氢番茄红素去饱和酶（PDS）和捕光多肽（如LHCBM6）的转录本水平大幅增加。低强度蓝光也能引发这些转录本水平的升高，而在三种合成低水平PHOT的不同RNA干扰菌株中，这种蓝光刺激受到抑制。藻类细胞暴露于低强度红光（RL）后，GSAT和LHCBM6转录本水平也会增加。转录本丰度的红光依赖性增加不受电子传递抑制剂3-(3,4-二氯苯基)-1,1-二甲基脲的影响，这意味着RL对转录本积累的影响不受细胞质氧化还原条件的控制，并且一种红光光感受器可能参与调节莱茵衣藻中特定光合作用相关基因的转录本水平。有趣的是，在PHOT RNA干扰菌株中，RL条件下升高的GSAT和LHCBM6转录本水平显著降低，这增加了蓝光和RL信号通路协同作用的可能性。微阵列实验表明，光系统（PS）I和II多肽的几种转录本水平也受到PHOT的调节。这些数据表明，在莱茵衣藻中，（i）PHOT参与蓝光介导的转录本积累变化，（ii）叶绿素（Chl）、类胡萝卜素、Chl结合蛋白和光合装置其他成分的合成同步化至少部分是通过PHOT介导的信号传导实现的，并且（iii）一种红光光感受器也可以影响与光合功能相关的某些转录本水平，尽管其作用需要正常水平的PHOT。
