Doctor of Philosophy, Pennsylvania State University (2018)
Jose Dinneny, Postdoctoral Faculty Sponsor
Mutations in the Pectin Methyltransferase QUASIMODO2 Influence Cellulose Biosynthesis and Wall Integrity in Arabidopsis thaliana.
The Plant cell
Pectins are abundant in the cell walls of dicotyledonous plants, but how they interact with other wall polymers and influence wall integrity and cell growth has remained mysterious. Here, we verified that QUASIMODO2 (QUA2) is a pectin methyltransferase and determined that QUA2 is required for normal pectin biosynthesis. To gain further insight into how pectin affects wall assembly and integrity maintenance, we investigated cellulose biosynthesis, cellulose organization, cortical microtubules, and wall integrity signaling in two mutant alleles of Arabidopsis thaliana QUA2, qua2 and tsd2. In both mutants, crystalline cellulose content is reduced, cellulose synthase particles move more slowly, and cellulose organization is aberrant. NMR analysis shows higher mobility of cellulose and matrix polysaccharides in the mutants. Microtubules in mutant hypocotyls have aberrant organization, and depolymerize more readily upon treatment with oryzalin or external force. The expression of genes related to wall integrity, wall biosynthesis, and microtubule stability is dis-regulated in both mutants. These data provide insights into how homogalacturonan is methylesterified upon its synthesis, the mechanisms by which pectin functionally interacts with cellulose, and how these interactions are translated into intracellular regulation to maintain the structural integrity of the cell wall during plant growth and development.
View details for DOI 10.1105/tpc.20.00252
View details for PubMedID 32883711
A Wall with Integrity: Surveillance and Maintenance of the Plant Cell Wall Under Stress.
The New phytologist
The structural and functional integrity of the wall needs to be constantly monitored and fine-tuned to allow for growth while preventing mechanical failure. Many studies have advanced our understanding of the pathways contributing to cell wall biosynthesis and how these pathways are regulated by external and internal cues. Recent evidence also supports a model in which certain aspects of the wall itself may act as growth-regulating signals. Molecular components of the signaling pathways that sense and maintain cell wall integrity have begun to be revealed, including signals arising in the wall, sensors that detect changes at the cell surface, and downstream signal transduction modules. Abiotic and biotic stress conditions set new contexts to study cell wall integrity, but the nature and consequences of wall disruptions by various stressors require further investigations. A deeper understanding of cell wall signaling will provide insights into the growth regulatory mechanisms that allow plants to survive in a changing environment. This article is protected by copyright. All rights reserved.
View details for DOI 10.1111/nph.16166
View details for PubMedID 31486535
Synergistic Pectin Degradation and Guard Cell Pressurization Underlie Stomatal Pore Formation.
Stomatal pores are vital for the diffusion of gasses into and out of land plants and are, therefore, gatekeepers for photosynthesis and transpiration. Although much published literature has described the intercellular signaling and transcriptional regulators involved in early stomatal development, little is known about the cellular details of the local separation between sister guard cells that give rise to the stomatal pore, or how formation of this pore is achieved. Using 3D time-lapse imaging, we found that stomatal pore formation in Arabidopsis thaliana is a highly dynamic process involving pore initiation and enlargement, and traverses a set of morphological milestones in 3D. Confocal imaging data revealed an enrichment of exocytic machinery, de-methyl-esterified pectic homogalacturonan (HG), and an HG-degrading enzyme at future pore sites, suggesting that both localized HG deposition and degradation might function in pore formation. By manipulating HG modification via enzymatic, chemical, and genetic perturbations in seedling cotyledons, we found that augmenting HG modification promotes pore formation, whereas preventing HG de-methyl-esterification delays pore initiation and inhibits pore enlargement. Through mechanical modeling and experimentation, we tested whether pore formation is an outcome of sister guard cells being pulled away from each other upon turgor increase. Osmotic treatment to reduce turgor pressure did not prevent pore initiation, but did lessen pore enlargement. Together, these data provide evidence that HG delivery and modification, and guard cell pressurization, make functional contributions to stomatal pore initiation and enlargement.
View details for DOI 10.1104/pp.19.00135
View details for PubMedID 30804009
- Mechanical Effects of Cellulose, Xyloglucan, and Pectins on Stomatal Guard Cells of Arabidopsis thaliana FRONTIERS IN PLANT SCIENCE 2018; 9
- Balancing Strength and Flexibility: How the Synthesis, Organization, and Modification of Guard Cell Walls Govern Stomatal Development and Dynamics FRONTIERS IN PLANT SCIENCE 2018; 9