| Cell separation/adhesion is critical in the life cycle of a plant as it is associated with many aspects of development. Cell separation/adhesion can be mediated by various classes of cell wall hydrolytic enzymes such as polygalaturonases (PG), beta-1,4endo(-,lucanases (cellulase), pectate lyases, pectin methylesterases and xyloglucan endo-transglycosylases resulting from modification of cell wall components.; In order to study cell separation/adhesion in plant development, two independent studies has been carried out. First, I examined the expression of 67 Arabidopsis PGs in six major tissue types, and then further analyzed these data in the evolutionary context with the rice PG family. In addition, the expression of five distinct floral organ abscission stages was examined to further understand the roles of PGs in floral organ abscission. There are nine distinct patterns of PG expression during abscission suggesting diverse but distinct roles of PGs in the abscission process. In addition. T-DNA disruption lines were identified for 4 PGs that showed specific up-regulation during floral organ abscission, and then further characterized. Second, using a novel delayed floral organ abscission mutant, dab4-1, I have studied the functions of DAB4 in not only floral organ abscission, but also during other developmental stages. I cloned DAB4 that is COI1, an F-box protein encoding gene. dab4-1 has a 1,537 by deletion in the genomic region of COI1. The original coi1-1 mutation demonstrates insensitivity to Jasmonates and defects in fertility due to lack of anther dehiscence. In dab4-1, however, there are additional phenotypic traits due to the different genetic background (WS ecotype) than coi1-1 (COL ecotype). WS specific traits such as strong apical dominance, epinastic leaf growth, and delayed meristem arrest are found only in dab4-1 (WS). However, these traits can be revealed by introgressing coi1-1 (COL) into the WS background. Both from genetic and microarray analysis, DAB4 shows epistasis while negatively regulating EIN2. Novel functions of COI1 in plant development and its role in floral organ abscission is discovered using dab4-1. |
