ABSCISIC-ACID AND JASMONIC ACID ACTIVATE WOUND-INDUCIBLE GENES IN POTATO THROUGH SEPARATE, ORGAN-SPECIFIC SIGNAL-TRANSDUCTION PATHWAYS

Mechanical damage to leaf tissue causes an increase in abscisic acid ( ABA) which in turn activates the biosynthesis of jasmonic acid (JA). T he resulting higher endogenous JA levels subsequently activate the exp ression of wound-inducible genes. This study shows that JA induces the expression of different sets of genes in roots and leaves of potato p lants. When roots of intact plants were treated with JA, high levels o f proteinase inhibitor II (pin2), cathepsin D inhibitor, leucine amino peptidase and threonine deaminase mRNAs accumulated in the systemic le aves. However, in the treated roots, very low, if any, expression of t hese genes could be detected. In contrast, a novel, root-specific pin2 homologue accumulated in the JA-treated root tissue which could not b e detected in leaves, either systemic or those directly treated with J A. Application of okadaic acid and staurosporine revealed that a prote in phosphorylation step is involved in the regulation of this differen tial response. In leaves, a protein phosphatase is required for the JA -induced expression of pin2 and the other genes analysed. This phospha tase activity is not necessary for the JA-induced expression of a pin2 homologue in roots, suggesting the existence of different transductio n pathways for the JA signal in these organs. The requirement of a pro tein phosphatase activity for JA-mediated gene induction has enabled i dentification of a JA-independent pathway for ABA induction of pin2 an d the other wound-inducible genes. This alternative pathway involves a protein kinase, and appears to be selective for wound-inducible genes . Our data suggest the presence of a complex, organ-specific transduct ion network for regulating the effects of the plant hormones ABA and J A on gene expression upon wounding.