The root system is formed by primary root, lateral roots, and adventitious roots (ARs). Auxin controls root biology. However, there is a patchy knowledge on regulatory mechanisms and signalling pathways interacting with auxin in rooting, including the action of jasmonates (JAs) and nitric oxide (NO). NO is a messenger in many aspects of plant differentiation, including rooting. NO may be non-stimulated/stimulated by auxin. Exogenous NO impacts ethylene (ET) production. Ethylene is another phytohormone positively/negatively involved in rooting, and treatments with NO donors show that NO may stimulate ET production and affect ET signalling. Both ET and NO are involved in AR formation and xylogenesis, the last program may occur as an alternative to ARs, starting from the same pericycle cells in the model plant Arabidopsis thaliana. Moreover, JAs and NO modulate each other production and JAs affect AR-formation interacting with auxin/ET, but JA/NO roles on xylogenesis are unclear. Indole-butyric acid (IBA) is the precursor of indole-acetic acid (IAA) and is the most AR inductive auxin in Arabidopsis. Both IBA and IAA also induce xylogenesis through an interaction with ET.
The IBA to IAA conversion is necessary for AR formation, and involves NO production. It is unknown if this conversion is also required for xylogenesis. Moreover, JA and NO interaction in xylogenesis needs investigation.
Our aim will be to determine the involvement of JA, ET, and NO in the control of the auxin-induced xylogenesis in comparison with adventitious rooting. To the aim, adventitious rooting and xylogenesis will be investigated in the hypocotyls of Arabidopsis seedlings exposed to various concentrations of the JA-donor methyl-JA (MeJA) with/without the application of an ET precursor or exogenous IBA/IAA. NO role in both programs will be evaluated by NO-donors/scavengers, and xylogenesis in the wild type compared with that in mutants blocked in either ET signalling or IBA-to-IAA conversion.
News for biotechnology.
i) To understand the molecular switching between rhizogenesis and xylogenesis will help to know the developmental control affecting root system architecture, with important consequences in improving rooting in recalcitrance species, and with positive consequences on plant fitness and phytoremediation applications.
ii) On the other hand, to understand the molecular control of ectopic xylem formation will be useful for biotechnological applications for example related to the production of biofuel.
Novelties for the advancement of knowledge.
i) New is also the possibility of identifying in stress molecules, such as jasmonates and nitric oxide, factors that positively and in a coordinated way mediate different forms of development in the plant.
ii) Last but not least, to understand the action of compounds/pathways that affect the changing in program, i.e., rhizogenesis vs xylogenesis, in the same pericycle cells, will be determinant for understanding the basis of stem cell condition in plants.