Jasmonic acid transient accumulation is needed for abscisic acid increase in citrus roots under drought stress conditions

Phytohormones are central players in sensing and signaling numerous environmental conditions like drought stress. In this work, an experimental system based on severe drought was established and hormone profiling together with gene expression of key enzymes involved in abscisic acid (ABA) and jasmonic acid (JA) biosynthesis was studied in roots of citrumelo CPB 4475 (a commercial citrus rootstock) plants. JA concentration transiently increased after a few hours of stress, returning to control levels 30 h after the onset of the condition. A more progressive ABA accumulation was observed, with the onset of this increase at the same time or right after the JA transient accumulation. Molecular data suggested that, at least, part of the hormonal regulation takes place at the biosynthetic level. These observations also pointed to a possible involvement of JA on ABA biosynthesis under stress. To test this hypothesis, JA and ABA biosynthesis were chemically inhibited and subsequently phenotypes rescued by the addition of exogenous hormones. Results showed that the early JA accumulation was necessary for the subsequent ABA increase in roots under stress whereas the opposite could not be stated. The model includes a burst of JA in roots of citrus under severe drought stress conditions that leads to a more progressive ABA accumulation that will induce later plant responses. The present work adds a new level of interaction between JA and ABA at the biosynthetic level that together with the previously described interaction between signal transduction cascades of the two hormones would allow plants to fine-tune specific responses to different stimuli.