Root systems show high degree of morphological diversity and plasticity. Adventitious roots (ARs) may be necessary to root system architecture and plant survival in particular environments, including polluted soils. The model dicot plant Arabidopsis thaliana has no/poor number of ARs at the hypocotyl base, while the monocot model plant rice has a fibrous root system with a high AR-number at the stem basal nodes. In Arabidopsis, auxin biosynthesis and transport positively affect AR formation and ectopic xylary formation starting from the same initial cells, but with a change in the cell division plane, and a cross-talk between jasmonates (JAs) and ethylene (ET) affects both programs. The AR response to soil pollutants, e.g. cadmium and arsenic, is similar in the two plants and similarly affected by JAs and auxin, involving nitric oxide (NO) signaling. In some species, brassinosteroids (BRs) regulate heavy metal stress tolerance, interact with auxin, JAs, and ET, and promote ARs by NO production through NOS-activity. However, BR role in the convergence of developmental and environmental signalling networks is far to be understood. BRASSINOSTEROID INSENSITIVE 2 kinase may be a possible candidate.
The Proposal aim is to investigate the interaction of BRs with JAs and ET in the switching between auxin-induced ARs and xylary cells in Arabidopsis and rice under pollutant soil conditions. To the aim, morpho-anatomical investigations, epifluorescence detection of NO and microtubule remodeling, exogenous BR and JAs +/-cadmium and arsenic treatments, molecular analysis of NOS genes will be carried out. Mutants in JA and BR synthesis/perception, and ET-signaling will be investigated, and reactive oxygen, nitrogen species and antioxidant enzymes monitored.
The Project challenge is to demonstrate that the initial cells of both ARs and xylary cells modulate their identity initiating either ARs or xylary cells as a developmental response of pollutant stress avoidance.
From this study we would like to gather information on how to manipulate adventitious rooting, by depressing competitive xylary cell formation, to increase basic knowledge on factors involved in cell identity changing in common between dicots and monocots, using Arabidopsis thaliana as a dicot model plant with a wide genetic/developmental background, but a poor AR formation, and rice as a monocot model, less studied than Arabidopsis, but with a wide adventitious root system, necessary to plant fitness. To study the mechanisms underlying BR-JA-regulated AR growth vs xylogenesis, in both optimal conditions and pollutant stress, will bring us closer to understanding the trade-off between growth and adaptation, and will help us strategize new approaches for creating smart root systems with efficient abilities even in the presence of pollutants that can sustain crop biomass and yield. In fact, modifying the root system architecture has been proposed as a pipeline to achieve a second green revolution and enhance crop yield (Den Herder et al. 2010), and will help develop predictive models for future crop improvement programmes.
The possible progress beyond the state of Art is to understand BR role on AR formation, not yet widely explored in Arabidopsis and rice, but also to shed light on the unknown role of the cross talk between JAs/BRs and auxin/ET on the cellular events leading to the change in identity between AR formation and xylogenesis in the same initial cells, and the signalling involved. Thus, the proposed project has both basic and applied research purposes. From one side, it is aimed to demonstrate that BRs might act upstream auxin to determine a change in cell fate programming in the hypocotyl pericycle (Arabidopsis) and parenchyma adjacent to the cylinder of vascular bundles (rice) being responsible, together with JAs, of modulating environmental (soil pollutants) and endogenous developmental signals by acting at the level of cell plate positioning and inducing asymmetric cell divisions. From the more applicative side, it is aimed at providing useful insights into optimization of rice crop in heavy metals/metalloids polluted soils. The Project¿s challenge is to demonstrate that the initial cells of both ARs and xylary cells exhibit a double commitment, initiating ARs instead xylary cells as a developmental mechanism caused by heavy metal(oid)s stress avoidance.
Thus, our idea is to get information from Arabidopsis to transfer to rice for improving root architecture in rice, as a premise for other cereals with similar root systems, e.g. wheat and maize, with the aim of increasing yield and resistance to pollutants up to the final goal of enhancing food quality and human health.
The social and economic outcome of this Project will be to improve the adventitious root system to improve land use and environment, improving human life.