Phytochromes consist of a N-terminal photosensory module and a C-terminal regulatory module. The photosensory core possesses three distinct domains: PAS, GAF and PHY; and the regulatory module is composed of PAS1、 PAS2 and HKRD domains. The bilin chromophore, which functions for light harvesting, is covalently attached to GAF domain whose conservation is one of the functional prerequisites for phytochrome photoconversion and signal transduction. PHY domain is crucial for tuning spectroscopic properties of the bound bilin. To make sure the purifying selection sites, the molecular evolution of 68 gymnosperm GAF domain sequences are assayed under the site model established. Results indicate there are 41 purifying selection sites found in GAF domain, 16 sites among them are located to the helical hairpin region of phytochrome. 15 sites lay within the beta strand region, and 3 sites are in the lasso loop region. The rest sites are beyond these regions.%光敏色素分子由位于N端的光感受区和位于C端的光调节区组成,光感受区包括PAS(Per/Arndt/Sim)、GAF(cG-MP phosphodiesterase/adenyl cyclase/FhlA)以及PHY(phytochrome domain)结构域,光调节区包括PAS1、PAS2以及HKRD(histidine kinase related domain)结构域.GAF结构域是发色团结合的部位,高度保守,该结构域的保守性是确保光敏色素光逆转和光信号转导等功能正常运行的先决条件之一.为了研究裸子植物PHY的GAF结构域经历纯化选择作用的位点,本文基于位点模型对裸子植物中68条GAF结构域序列所受到的选择压力进行分析.结果表明:在GAF结构域中,有41个位点经历了纯化选择作用,其中有16个位于α螺旋结构区,有15个位于β折叠结构区,有3个位于套索区,另外7个位点位于这些结构之间,这说明,相对于其他区域,a区和β区在功能上更为保守.
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