Characterization of the ELMO2 Protein that Mediates Cell Adhesion in Arabidopsis thaliana

The binding of adjacent cells to one another, or cell adhesion, is critical for the growth and development of multicellular organisms. In plant cells, much evidence suggests that the amount and modification of pectin in the cell wall largely determines how well cell adhesion occurs. ELMO1 is a Golgi protein involved in pectin-mediated cellular adhesion, and mutations in ELMO1 lead to disrupted cell organization in Arabidopsis. ELMO1 is predicted to be a scaffold for pectin biosynthesis enzymes, and thus its absence leads to the adhesion-defective phenotype of elmo1-/- plants. There are four other ELMO homologues (ELMO2,3,4 and 5) which remain to be characterized as to their function and role in cell adhesion. This thesis focuses on the characterization of ELMO2, which has 79% amino acid similarity with ELMO1. A genetic analysis that evaluated elmo2 double mutants revealed that ELMO2 and ELMO1 have redundant functions. elmo1-/-/2-/- double mutants, but not elmo2-/- or elmo1-/- single mutants, have reduced tensile strengths. While elmo1-/- phenotypes are most pronounced in liquid media, they are partially rescued by growth on agar, suggesting a role of turgor in maintaining cell adhesion. Like ELMO1, ELMO2-GFP colocalizes with Golgi markers. The results suggest that like ELMO1, ELMO2 also functions as a scaffold for pectin biosynthesis enzymes in the Golgi.