Not Only Systemin Prosystemin Harbors Other Active Regions Able to Protect Tomato Plants

Prosystemin is a 200-amino acid precursor expressed in Solanaceae plants which releases at the C-terminal part a peptidic hormone called Systemin in response to wounding and herbivore attack. We recently showed that Prosystemin is not only a mere scaffold of Systemin but, even when deprived of Systemin, is biologically active. These results, combined with recent discoveries that Prosystemin is an intrinsically disordered protein containing disordered regions within its sequence, prompted us to investigate the N-terminal portions of the precursor, which contribute to the greatest disorder within the sequence. To this aim, PS1-70 and PS1-120 were designed, produced, and structurally and functionally characterized. Both the fragments, which maintained their intrinsic disorder, were able to induce defense-related genes and to protect tomato plants against <em>Botrytis cinerea</em> and <em>Spodoptera littoralis</em> larvae. Intriguingly, the biological activity of each of the two N-terminal fragments and of Systemin is similar but not quite the same and does not show any toxicity on experimental non-targets considered. These regions account for different anti-stress activities conferred to tomato plants by their overexpression. The two N-terminal fragments identified in this study may represent new promising tools for sustainable crop protection.原系统素（Prosystemin）是一种由茄科（Solanaceae）植物表达的200氨基酸残基前体蛋白，在遭遇机械损伤或草食动物侵袭时，可从其C端释放一种名为系统素（Systemin）的肽类激素。我们近期的研究表明，原系统素并非仅作为系统素的简单支架蛋白，即便去除系统素序列，其本身仍具有生物学活性。结合近期关于原系统素是一种内在无序蛋白（intrinsically disordered protein）、其序列内包含多个无序区域的发现，我们针对该前体的N端区域展开了研究——该区域在整体序列中无序占比最高。为此，我们设计并制备了PS1-70与PS1-120两个片段，并对其结构与功能进行了表征。这两个片段均保留了内在无序特性，能够诱导防御相关基因的表达，且可保护番茄植株免受灰葡萄孢（Botrytis cinerea）与斜纹夜蛾（Spodoptera littoralis）幼虫的侵害。值得注意的是，两个N端片段与系统素的生物学活性虽相似却并非完全一致，且对本次研究所涉及的实验非靶标生物无任何毒性。这些区域可介导过表达状态下番茄植株获得的多样抗逆活性。本研究中鉴定出的这两个N端片段，有望成为可持续作物保护领域的新型实用工具。