Chen Hsien-Jung, Huang Dong-Jiann, Hou Wen-Chi, Liu Jih-Shiou, Lin Yaw-Huei
Department of Horticulture, Chinese Culture University, 111 Taipei, Taiwan, ROC.
J Plant Physiol. 2006 Jul;163(8):863-76. doi: 10.1016/j.jplph.2005.08.008. Epub 2005 Oct 24.
Granulins are a family of evolutionarily ancient proteins that are involved in regulating cell growth and division in animals. In this report a full-length cDNA, SPCP3, was isolated from senescent leaves of sweet potato (Ipomoea batatas). SPCP3 contains 1389 nucleotides (462 amino acids) in its open reading frame, and exhibits high amino acid sequence homologies (ca. 64-73.6%) with several plant granulin-containing cysteine proteases, including potato, tomato, soybean, kidney bean, pea, maize, rice, cabbage, and Arabidopsis. Gene structural analysis shows that SPCP3 encodes a putative precursor protein. Via cleavage of the N-terminal propeptide, it generates a protein with 324 amino acids (from the 139th to the 462nd amino acid residues), which contains two main domains: the conserved catalytic domain with the putative catalytic residues (the 163rd Cys, 299th His and 319th Asn) and the C-terminal granulin domain (from the 375th to the 462nd amino acid residues). Semi-quantitative RT-PCR and protein gel blot hybridization showed that SPCP3 gene expression was enhanced significantly in natural senescent leaves and in dark- and ethephon-induced senescent leaves, but was almost undetectable in mature green leaves, veins, and roots. Phylogenic analysis showed that SPCP3 displayed close association with a group of plant granulin-containing cysteine proteases which have been implied to be involved in programmed cell death. In conclusion, sweet potato SPCP3 is a functional, senescence-associated gene. Its mRNA and protein levels were significantly enhanced in natural and induced senescing leaves. The physiological role and/or function of SPCP3 associated with programmed cell death during leaf senescence were also discussed.
颗粒蛋白是一类进化上古老的蛋白质家族，参与动物细胞生长和分裂的调控。在本报告中，从甘薯（Ipomoea batatas）衰老叶片中分离出一个全长cDNA，即SPCP3。SPCP3的开放阅读框包含1389个核苷酸（462个氨基酸），与几种含颗粒蛋白的植物半胱氨酸蛋白酶（包括马铃薯、番茄、大豆、菜豆、豌豆、玉米、水稻、卷心菜和拟南芥）表现出较高的氨基酸序列同源性（约64 - 73.6%）。基因结构分析表明，SPCP3编码一种假定的前体蛋白。通过切割N端前肽，它产生一种含324个氨基酸的蛋白（从第139个到第462个氨基酸残基），该蛋白包含两个主要结构域：具有假定催化残基（第163个半胱氨酸、第299个组氨酸和第319个天冬酰胺）的保守催化结构域和C端颗粒蛋白结构域（从第375个到第462个氨基酸残基）。半定量RT-PCR和蛋白质凝胶印迹杂交表明，SPCP3基因在自然衰老叶片以及黑暗和乙烯利诱导的衰老叶片中表达显著增强，但在成熟绿叶、叶脉和根中几乎检测不到。系统发育分析表明，SPCP与一组含颗粒蛋白的植物半胱氨酸蛋白酶密切相关，这些蛋白酶被认为参与程序性细胞死亡。总之，甘薯SPCP3是一个与衰老相关的功能基因。其mRNA和蛋白质水平在自然和诱导衰老的叶片中显著增强。还讨论了SPCP3在叶片衰老过程中与程序性细胞死亡相关的生理作用和/或功能。
