RESUMEN
The plant signaling hormones salicylic acid (SA) and jasmonic acid (JA) are regulators of inducible defenses that are activated upon pathogen or insect attack. Cross-talk between SA- and JA-dependent signaling pathways allows a plant to finely tune its response to the attacker encountered. In Arabidopsis, pharmacological experiments revealed that SA exerts a strong antagonistic effect on JA-responsive genes, such as PDF1.2, indicating that the SA pathway can be prioritized over the JA pathway. SA-mediated suppression of the JA-responsive PDF1.2 promoter was exploited for setting up a genetic screen aiming at the isolation of signal transduction mutants that are impaired in this cross-talk mechanism. The PDF1.2 promoter was fused to the herbicide resistance gene BAR to allow for life/death screening of a population of mutagenized transgenic plants. Non-mutant plants should survive herbicide treatment when methyl jasmonate (MeJA) is applied, but suppression of the JA response by SA should be lethal in combination with the herbicide. Conversely, crucial SA/JA cross-talk mutants should survive the combination treatment. SA effectively suppressed the expression of the PDF1.2::BAR transgene. However, suppression of the BAR gene did not result in suppression of herbicide resistance. Hence, a screening method based on quantitative differences in the expression of a reporter gene may be better suited to identify SA/JA cross-talk mutants. Here, we demonstrate that the PDF1.2::GUS reporter will be excellently suited in this respect.
RESUMEN
In Arabidopsis thaliana the R2R3-MYB transcription factor family consists of over 100 members and is implicated in many biological processes, such as plant development, metabolism, senescence, and defense. The R2R3-MYB transcription factor gene AtMYB102 has been shown to respond to salt stress, ABA, JA, and wounding, suggesting that AtMYB102 plays a role in the response of plants to dehydration after wounding. Here, we studied the role of AtMYB102 in the response of A. thaliana to feeding by larvae of the white cabbage butterfly Pieris rapae. A. thaliana reporter lines expressing GUS under control of the AtMYB102 promoter revealed that AtMYB102 is expressed locally at the feeding sites of herbivore-damaged leaves, but not systemically in uninfested plant parts. Knockout AtMYB102 transposon-insertion mutant plants (myb102) allowed a faster development of P. rapae caterpillars than wild-type Col-0 plants. Moreover, the number of caterpillars that had developed into pupae within 14 days was significantly higher on myb102, indicating that in wild-type plants AtMYB102 contributes to basal resistance against P. rapae feeding. Microarray analysis of wild-type Col-0 and AtMYB102 overexpressing 35S::MYB102 plants revealed a large number of differentially expressed genes. Besides several defense-related genes, a relatively large number of genes is associated with cell wall modifications.
RESUMEN
Salicylic acid is an important signalling molecule involved in both locally and systemically induced disease resistance responses. Recent advances in our understanding of plant defence signalling have revealed that plants employ a network of signal transduction pathways, some of which are independent of salicylic acid. Evidence is emerging that jasmonic acid and ethylene play key roles in these salicylic acid-independent pathways. Cross-talk between the salicylic acid-dependent and the salicylic acid-independent pathways provides great regulatory potential for activating multiple resistance mechanisms in varying combinations.