The plant elicitor peptide (Pep) is a signal that promotes local defence responses, in contrast to the systemin peptide that is required to promote the systemic defence response in tomato and other nightshades. Both peptides are encoded as precursors (ProSys and ProPep) that are induced by local wounding (for example, by insect herbivores or fungal and bacterial pathogens that cause lesions at the infection site). Systemin, the first plant peptide hormone to be discovered, binds to the systemin receptor (SYR1 and SYR2) upon wounding and promotes long-range signalling that may include jasmonate, ethylene or volatile organic compounds. By contrast, Pep binds to the Pep receptors (PEPRs), the homologue of which in tomato is called PEPR1/2 ORTHOLOG RECEPTOR-LIKE KINASE 1 (PORK1) and induces a local defence response. Although the roles of systemin and Pep in defence responses against herbivores and pathogens were established, their potential function in regeneration of the physical wounding caused by these herbivores and pathogens was unknown.

The researchers find that mutants of the tomato systemin precursor are not affected in the regeneration response induced by wounding. However, mutants of the precursor of Pep lose the regeneration capacity of hypocotyl explants with abolished callus formation and shoot regeneration. Both precursor overexpression and exogenous application of recombinant mature Pep enhance callus formation and shoot regeneration. These observations suggest that Pep, but not systemin, is required for the regeneration response, and Pep was renamed REGENERATION FACTOR 1 (REF1). They show that the regeneration response induced by REF1 depends on the PORK1 receptor. REF1–PORK1 signalling targets WIND1, the expression of which is diminished in mutants of either REF1 or PORK1. Interestingly, WIND1 activates the promoter of the Pep precursor, which causes positive feedback. The enhancing effect of recombinant REF1 on shoot regeneration is not limited to tomato, and the authors show that application of recombinant orthologues of maize, wheat and soybean has similar effects. This suggests that the role of REF1 in shoot regeneration is conserved and that external application of a regeneration factor may be a suitable tool to enhance regeneration efficiency after transformation of recalcitrant crop species.

植物激发肽 (Pep) 是促进局部防御反应的信号，而系统素肽则需要促进番茄和其他茄科植物的全身防御反应。这两种肽均被编码为前体（ProSys 和 ProPep），由局部损伤（例如，昆虫食草动物或在感染部位引起病变的真菌和细菌病原体）诱导。系统素是第一个被发现的植物肽激素，在受伤时与系统素受体（SYR1 和 SYR2）结合，并促进远程信号传导，其中可能包括茉莉酸、乙烯或挥发性有机化合物。相比之下，Pep 与 Pep 受体 (PEPR) 结合，其在番茄中的同源物称为 PEPR1/2 直系受体样激酶 1 (PORK1)，并诱导局部防御反应。尽管系统素和 Pep 在针对食草动物和病原体的防御反应中的作用已经确定，但它们在这些食草动物和病原体造成的身体伤害再生中的潜在功能尚不清楚。

研究人员发现，番茄系统素前体的突变体在受伤引起的再生反应中不受影响。然而，Pep 前体的突变体失去了下胚轴外植体的再生能力，并消除了愈伤组织形成和芽再生。重组成熟 Pep 的前体过度表达和外源应用均增强愈伤组织形成和芽再生。这些观察结果表明，再生反应需要 Pep，而不是系统素，因此 Pep 被重新命名为再生因子 1 (REF1)。他们表明 REF1 诱导的再生反应取决于 PORK1 受体。 REF1-PORK1 信号传导以 WIND1 为目标，其表达在 REF1 或 PORK1 突变体中减弱。有趣的是，WIND1 激活 Pep 前体的启动子，从而引起正反馈。重组REF1对芽再生的增强作用不仅限于番茄，作者表明，玉米、小麦和大豆的重组直系同源物的应用也具有类似的效果。这表明 REF1 在芽再生中的作用是保守的，并且外部应用再生因子可能是提高难驯作物物种转化后再生效率的合适工具。