Doctor of Philosophy (PhD)
Biological sciences department
Abscisic acid (ABA) is a plant hormone that triggers a signaling transduction in response to drought, salinity, and cold. The core components in the ABA signaling pathway that lead to downstream ABA responses have been identified.
Phosphatidic acid (PA) is a membrane phospholipid that is involved in the signaling pathway for ABA-induced stomatal closure. We tested whether PA is involved in the signaling pathway for ABA-induced gene expression as well, using model plant Arabidopsis thaliana. We selected the RD29A gene which is a canonical drought gene that is induced by ABA. We found that PA is not involved in the signaling pathway for ABA-induced gene expression even though core components involved in the ABA signaling pathway are shared between stomatal closure and gene expression. We propose that some of the homologous phosphatases that are not inhibited by PA, lead to ABA-induced gene expression.
To advance the finding that PA is involved in the signaling pathway for ABA-induced stomatal closure, we created a PA biosensor based on dimerization-dependent fluorescent proteins. The biosensor allowed us to determine the spatiotemporal production of PA in Arabidopsis plants when exposed to ABA or sodium chloride (NaCl). The PA biosensor showed that there was an increase in PA concentrations with ABA and NaCl on the plasma membrane within 10 minutes. On the internal membranes, PA concentrations increased on exposure to ABA but not to NaCl. These results suggest that the formation of transient PA on different membranes is specific to the stress.
To further investigate the connectivity of core components in the ABA signaling pathway and identify the next research frontiers in the ABA-signaling pathway, we constructed a dynamic model with a set of ordinary differential equations. Computational analysis predicted that the translation rate constant of protein phosphatases (PP2Cs), which are negative regulators in the pathway, determine the kinetics of ABA-mediated gene expression. Changes in the PP2C translation rate constant altered the levels of gene expression and the peak time point of expression. We propose that studying alteration of translation rates by ABA will help grow plants that are tolerant to drought.
Ndathe, Ruth Wanjiru, "Insights into Abscisic Acid and Phosphatidic Acid Signal Transduction Dynamics in Arabidopsis thaliana" (2021). LSU Doctoral Dissertations. 5692.