Ivan Paponov received his Ph. D. degree from the Moscow Timyrazev Academy in Russia in 1992. Following postdoctoral periods at Moscow Lomonosov University and the University of Hohenheim in Stuttgart, he worked on genotypic aspects of mineral nutrition in higher plants. In 2002, he began research at the University of Freiburg in the field of auxin transport and auxin signalling in which he applied the chemical genetics and bioinformatics tools. He is currently a researcher at the Norwegian Institute of Bioeconomy. His research focus is on plant adaptation to different environments, with emphasis on the molecular responses of plants to light, CO2 concentration and nitrogen.
During the presentation I will discuss about the mechanism of plant adaptation to abiotic stresses. Specifically, I will address to the observation that different abiotic stresses all seem to modulate plant growth in a way that generates a similar plant phenotype – one that helps to attenuate the adverse effects of stress and increases the chances of plant survival. This similarity of plant phenotypes under different stresses has been assumed to reflect a common mechanism of plant adaptation in which reactive oxygen species (ROS) and plant hormone auxin each play important roles. ROS are well known and extensively investigated inhibitors of auxin activity, acting via auxin oxidation, attenuation of signalling and inhibition of auxin transport. However, the mechanisms by which auxin affects ROS are less well understood, which limits our understanding of cross-talk between ROS and auxin. Therefore, in my talk I will focus on mechanism of auxin action on ROS. I will show quantitative determination of ROS production after auxin treatments, which demonstrate that auxin differentially regulates the levels of ROS in roots: it decreases cell wall levels of superoxide and increases hydrogen peroxide levels. Therefore, ROS–auxin cross-talk occurs by the operation of positive and negative feedback loops between ROS and IAA. Positive (double negative) feedback consists of inhibition of auxin activity by ROS and reduction of superoxide levels by auxin. This positive feedback loop includes the regulation of plastid gene expression, including upregulation by superoxide and inhibition by auxin. Negative feedback loops consists of inhibition of auxin action by ROS and stimulation of H2O2 production by auxin. General oxidative response genes were highly over-represented among the auxin-induced genes, possibly due to stimulation of H2O2 production by auxin and the presence of binding sites in the promoters of auxin responsive genes for transcription factors WRKY and bHLH, which are involved in ROS signalling. Expression analysis of ROS-related genes that respond to auxin showed that peroxidases are the best candidates for the differential production of ROS and the guiding of feedback loops between ROS and auxin.
Conclusions: Differential induction of ROS by auxin and regulation of auxin activity by ROS create a combination of positive and negative feedback loops between ROS and auxin to allow adjustment of plant growth to environmental stress conditions.