Schaller A, Ryan C A
Institute of Biological Chemistry, Washington State University, Pullman 99164-6340, USA.
Bioessays. 1996 Jan;18(1):27-33. doi: 10.1002/bies.950180108.
Insect and pathogen attacks activate plant defense genes within minutes in nearby cells, and within hours in leaves far distant from the sites of the predator attacks. A search for signal molecules involved in both the localized and distal signalling has resulted in the identification of an 18-amino-acid polypeptide, called systemin, that activates defense genes in leaves of tomato plants when supplied at levels as low as fmols/plant. Several lines of evidence support a role for systemin as a wound hormone. As with animal polypeptide hormones, systemin is derived from a larger precursor protein, called prosystemin, by limited proteolysis. Systemin has been shown by autoradiography to be phloemmobile and, by antisense technology, to be an essential component of the wound-inducible, systemic signal transduction system leading to the transcriptional activation of the defensive genes. A search for the receptor of systemin has led to the identification in plant plasma membranes of a systemin-binding protein. However, this protein has properties not of a receptor, but of a furin-like proteinase that cleaves systemin into smaller polypeptides. Systemin and its precursor prosystemin provide prototypes for the emerging possibilities that polypeptide hormones may have broad roles in signalling environmental stress responses, and in regulating plant growth and development as well.
昆虫和病原体攻击会在几分钟内激活附近细胞中的植物防御基因，在数小时内激活远离捕食者攻击部位的叶片中的防御基因。对参与局部和远端信号传导的信号分子进行的研究，已鉴定出一种由18个氨基酸组成的多肽，称为系统素，当以低至飞摩尔/植物的水平供应时，它能激活番茄植株叶片中的防御基因。几条证据支持系统素作为一种创伤激素的作用。与动物多肽激素一样，系统素是由一种称为前系统素的更大的前体蛋白通过有限的蛋白水解作用产生的。放射自显影显示系统素可在韧皮部移动，通过反义技术表明它是创伤诱导的全身信号转导系统的重要组成部分，该系统导致防御基因的转录激活。对系统素受体的研究已导致在植物质膜中鉴定出一种系统素结合蛋白。然而，这种蛋白不具有受体的特性，而是具有一种将系统素切割成较小多肽的弗林蛋白酶样蛋白酶的特性。系统素及其前体前系统素为多肽激素可能在信号传导环境应激反应以及调节植物生长和发育中发挥广泛作用的新可能性提供了原型。
