Analysis of the signalling mechanisms involved in Cell Wall Integrity maintenance in A.thaliana

Abstract

The plant cell wall is a dynamic structure that has an integral role during plant development and responses to biotic and abiotic stresses. A cell wall integrity (CWI) maintenance mechanism in plants has been inferred. The aim of this study was to investigate the signalling mechanism that regulates the response of Arabidopsis thaliana to CWI impairment. Here I show that JA and SA levels increase after 3 and 5 hours (respectively) of CWI impairment. In order to determine the downstream functions of the different signalling mechanisms and their cross-talk upon CWI impairment; lignin deposition, JA & SA induction and root growth inhibition (RGI) phenotypes were used as downstream readouts. My results show that ROS are required for lignin deposition whereas JA & SA-based mechanisms are required to inhibit lignin deposition. ROS and JA act antagonistically to regulate downstream lignin deposition. In addition, a bi-phasic ROS-based signal is induced after CWI impairment, with the initial signal required for JA induction and the later signal required for inhibition of JA induction. H2O2 increased at the plasma membrane in the elongation zone of the root during CWI impairment, as determined by the genetically encoded probe HyPer. The functions of several RLKs in CWI maintenance were investigated. These included BAK1 and BIK1. Most of the mutant RLKs investigated affected one or two of the downstream readouts, highlighting the complexity of CWI signalling and demonstrating the involvement of elements of the innate immunity signalling. However, THE1 and XII7, mutant seedlings display altered responsiveness to all CWI impairment downstream readouts. These results suggest that these two RLKs represent key regulators of CWI maintenance. To summarise, the research piresented here has provided novel insights into the signalling mechanisms mediating the response to CWI impairment; has clarified the involvement of several RLKs whose functions had not been defined before and has shown that THE1 and XII7 are key regulators required for mediating all responses to CWI impairment.