Revealing Missing Pieces of the Puzzle: The Possible Function of Candidate Genes in the Cell Wall Integrity Maintenance mechanism in Arabidopsis thaliana

Abstract

As sessile organisms, plants depend on mechanisms to sense and respond to stressful conditions such as biotic and abiotic factors. A complex mechanism referred to as the cell wall integrity maintenance (CWI) mechanism, has been shown to actively monitor the state of the plant cell wall and maintain its integrity. Turgor pressure and the cell wall are interacting to enable cell expansion and previous results have implicated turgor pressure also in CWI maintenance. However, mode of action of this mechanism and the function of turgor in this context are not well-understood. The Host research group carried out a transcriptomics analysis to identify genes maintaining plant CWI during development, which are also responsive to turgor manipulation. In this thesis a functional characterization of two turgor-sensitive candidate genes (PLANT GLYCOGENIN-LIKE STARCH INITIATION PROTEIN 7 (PGSIP7) and RECEPTOR LIKE PROTEIN 12 (RLP12)) identified through the transcriptomics analysis was initiated. Because of its sequence similarity PGSIP8 was also included. The analysis involved mainly phytohormone measurements, lignin quantification, qRT-PCR-based gene expression analysis and production of different constructs for gene expression and localization studies. qRT-PCR-based expression analysis confirmed that expression of the three genes increases in seedlings exposed to cell wall damage (CWD). For PGSIP7, a PGSIP7::GUS reporter was generated allowing a promoter activity analysis in the future. Differences between pgsip7 knock-outs and wild-type seedlings were observed in response to CWD but they were not reproducible statistically significant. This might be due to functional redundancy. Therefore, the phenotypic analysis must be repeated with pgsip8 and the pgsip7pgsip8 knock-out seedlings. A RLP12::GUS reporter showed expression in seedling roots, which increased in the elongation zone and vascular tissue in response to CWD suggesting a role for RLP12 in root development and CWI maintenance. Results from phytohormone and lignin measurements in rlp12 knock-out and RLP12 overexpressing seedlings implicated the gene in CWI monitoring. These results show that all three genes PGSIP7, PGSIP8 and RLP12 responds to CWD and further suggests a role for RLP12 in root development and CWI maintenance.