Exploring the roles of CYCD3s and AINTEGUMENTA in the control of plant growth and development

Regulation of higher plant growth and development involves the control of cell growth and division, since plant cells are immobile. A key point of plant cell cycle control is the G1 to S transition, which is promoted by CyclinD/CDK complexes. Several subgroups of D-type cyclins exist in higher plants, and the genes encoding these proteins appear to be under environmental and developmental regulation. In Arabidopsis, the CYCD3 subgroup consists of three members. The roles that these genes play in growth and development are explored, and the interaction between these genes and other factors controlling plant growth and development are investigated. A role for CYCD3;1 and its putative regulator ANT in root auxiliary meristem development is shown. However, whilst ant and cycd3;1 mutants shared some phenotypes, such as increased petal cell size, reduced leaf cell number and reduced root thickness, double mutants exhibited additive phenotypes, suggesting that there is not a strong regulation of CYCD3;1 by ANT. Supporting this, a physical interaction between ANT and a putative ANT-binding site from the CYCD3;1 promoter was not detected, and evidence of CYCD3;1 transcription regulation by ANT was weak. Supporting an alternative hypothesis, evidence of coregulation of ANT and CYCD3;1 by cytokinins in roots is provided. The expression of these genes in roots required cytokinins and appeared to be correlated. Roles for all three CYCD3s and the ERECTA (ER) kinase in the regulation of primary vascular tissue development are described, and genetic evidence of a link between CYCD3s and ER is provided. These genes appear to be required for cell division events in the procambium lineage. Furthermore, ER was also found to regulate secondary growth. Thus five novel regulators of root development have been identified, and important knowledge regarding mechanisms of lateral aerial organ size control has been gained