Physiological roles of the light, oxygen, or voltage domains of phototropin 1 and phototropin 2 in Arabidopsis
Physiological roles of the light, oxygen, or voltage domains of phototropin 1 and phototropin 2 in Arabidopsis
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DOI：
10.1104/pp.106.089839
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发表时间：
2007-01-01
期刊：
影响因子：
7.4
通讯作者：
Briggs, Winslow R.
中科院分区：
文献类型：
--
作者：
Cho, Hae-Young;Tseng, Tong-Seung;Briggs, Winslow R.
向光素（phot1 和 phot2）是植物蓝光受体，可介导拟南芥 (Arabidopsis thaliana) 的向光性、叶绿体运动、气孔打开、黄化幼苗生长的快速抑制和叶片扩张。它们的 N 末端区域包含两个光、氧或电压 (LOV) 结构域，这些结构域结合黄素单核苷酸，并在光激发时在保守的半胱氨酸和黄素单核苷酸发色团之间形成共价加合物。 C 末端区域包含丝氨酸/苏氨酸激酶结构域，可催化蓝光激活的自磷酸化。在这里，我们用花椰菜花叶病毒 35S 启动子驱动的 PHOT 表达构建体转化了 phot1 phot2 (phot1-5 phot2-1) 双突变体。这些构建体编码野生型趋光素或具有一个或两个 LOV 结构域半胱氨酸突变以阻断其光化学作用的趋光素。我们在八个转化体类别中的每一个类别中选择了多个品系以进行进一步的生理分析。具体来说，我们研究了 LOV1 和 LOV2 在向光性和叶片扩展方面是否具有相同或不同的功能。我们的结果表明，phot1 的 LOV2 结构域在向光性和叶片扩展中起主要作用，phot2 的 LOV2 结构域也是如此。没有观察到 phot1 的 LOV1 结构域具有向光性或叶片扩张的互补性。然而，意外地发现phot2 LOV1在相当大的水平上补充了向光性。类似地，携带两个 LOV 结构域均失活的 PHOT 转基因的转化体对高通量率蓝光产生了强烈的曲率。然而，我们发现 phot2-1 突变体是有漏洞的，并且产生少量的全长 phot2 蛋白。体外实验表明，功能性 phot2 和失活 phot1 分子之间可能发生交叉磷酸化。这种机制可能发生在体内，因此解释了在两个 lov 结构域失活的 PHOT 转基因中观察到的功能活性。讨论了该机制对于向光素功能的影响。
Phototropins (phot1 and phot2) are plant blue-light receptors that mediate phototropism, chloroplast movement, stomatal opening, rapid inhibition of growth of etiolated seedlings, and leaf expansion in Arabidopsis (Arabidopsis thaliana). Their N-terminal region contains two light, oxygen, or voltage (LOV) domains, which bind flavin mononucleotide and form a covalent adduct between a conserved cysteine and the flavin mononucleotide chromophore upon photoexcitation. The C-terminal region contains a serine/threonine kinase domain that catalyzes blue-light-activated autophosphorylation. Here, we have transformed the phot1 phot2 (phot1-5 phot2-1) double mutant with PHOT expression constructs driven by the cauliflower mosaic virus 35S promoter. These constructs encode either wild-type phototropin or phototropin with one or both LOV-domain cysteines mutated to block their photochemistry. We selected multiple lines in each of the eight resulting categories of transformants for further physiological analyses. Specifically, we investigated whether LOV1 and LOV2 serve the same or different functions for phototropism and leaf expansion. Our results show that the LOV2 domain of phot1 plays a major role in phototropism and leaf expansion, as does the LOV2 domain of phot2. No complementation of phototropism or leaf expansion was observed for the LOV1 domain of phot1. However, phot2 LOV1 was unexpectedly found to complement phototropism to a considerable level. Similarly, transformants carrying a PHOT transgene with both LOV domains inactivated developed strong curvatures toward high fluence rate blue light. However, we found that the phot2-1 mutant is leaky and produces a small level of full-length phot2 protein. In vitro experiments indicate that cross phosphorylation can occur between functional phot2 and inactivated phot1 molecules. Such a mechanism may occur in vivo and therefore account for the functional activities observed in the PHOT transgenics with both lov domains inactivated. The implications of this mechanism with respect to phototropin function are discussed.