Proteomic analysis of young leaves at three developmental stages in an albino tea cultivar.

White leaf No.1 is a typical albino tea cultivar grown in China and it has received increased attention in recent years due to the fact that white leaves containing a high level of amino acids, which are very important components affecting the quality of tea drink. According to the color of its leaves, the development of this tea cultivar is divided into three stages: the pre-albinistic stage, the albinistic stage and the regreening stage. To understand the intricate mechanism of periodic albinism, a comparative proteomic approach based on two-dimensional electrophoresis (2-DE) and mass spectrometry was adopted first time to identify proteins that changed in abundance during the three developmental periods. The 2-DE results showed that the expression level of 61 protein spots varied markedly during the three developmental stages. To analyze the functions of the significantly differentially expressed protein spots, 30 spots were excised from gels and analyzed by matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry. Of these, 26 spots were successfully identified. All identified protein spots were involved in metabolism of carbon, nitrogen and sulfur, photosynthesis, protein processing, stress defense and RNA processing, indicating these physiological processes may play crucial roles in the periodic albinism. Quantitative real-time RT-PCR analysis was used to assess the transcriptional level of differentially expressed proteins. In addition, the ultrastructural studies revealed that the etioplast-chloroplast transition in the leaf cell of White leaf No. 1 was inhibited and the grana in the chloroplast was destroyed at the albinistic stage. In this work, the proteomic analysis revealed that some proteins may have important roles in the molecular events involved in periodic albinism of White leaf No. 1 and identificated many attractive candidates for further investigation. In addition, the ultrastructural studies revealed that the change in leaf color of White leaf No. 1 might be a consequence of suppression of the etioplast-chloroplast transition and damage to grana in the chloroplast induced by temperature. These results provide much useful information to improve our understanding of the mechanism of albinism in the albino tea cultivar.

“白叶1号”是中国种植的一种典型的白化茶树品种，近年来因其叶片含较高水平的氨基酸而受到越来越多的关注，氨基酸是影响茶饮品质量的重要成分。根据其叶片颜色，该茶树品种的发育分为三个阶段：白化前期、白化期和返绿期。为了解周期性白化的复杂机制，首次采用基于双向电泳（2 - DE）和质谱的比较蛋白质组学方法来鉴定在三个发育时期丰度发生变化的蛋白质。 2 - DE结果显示，61个蛋白点在三个发育阶段的表达水平有显著差异。为分析显著差异表达蛋白点的功能，从凝胶中切取30个点，并用基质辅助激光解吸电离 - 飞行时间 - 串联质谱进行分析。其中，26个点被成功鉴定。所有已鉴定的蛋白点都参与碳、氮和硫的代谢、光合作用、蛋白质加工、胁迫防御以及RNA加工，表明这些生理过程可能在周期性白化中起关键作用。采用实时定量RT - PCR分析来评估差异表达蛋白质的转录水平。此外，超微结构研究表明，“白叶1号”叶片细胞中的黄化质体 - 叶绿体转变在白化期受到抑制，叶绿体中的基粒遭到破坏。 在这项工作中，蛋白质组学分析表明，一些蛋白质可能在“白叶1号”周期性白化所涉及的分子事件中起重要作用，并确定了许多有吸引力的候选对象以供进一步研究。此外，超微结构研究表明，“白叶1号”叶片颜色的变化可能是温度诱导的叶绿体中黄化质体 - 叶绿体转变受抑制以及基粒受损的结果。这些结果为增进我们对白化茶树品种白化机制的理解提供了许多有用信息。