| This thesis is an investigation of the roles of the paralog GATA transcription factors GNC and CGA1 in plants. Agricultural productivity is related to the ability of crop plants to fix carbon which is achieved through the chloroplast. Chloroplast numbers and chlorophyll level are controlled by environmental factors including light amount and quality as well as the available nitrogen. The Arabidopsis paralog GATA transcription factors GNC and CGA1 were shown to modulate the chloroplast number, chlorophyll and leaf starch content in proportion to their transcript level. In transgenic lines with altered expression of either GNC or CGA1, leaf chloroplast number and chlorophyll content varied and this variation was dependent on the amount of light and nitrate supplied. Expression of GNC and CGA1 was found to correlate with the expression of Glutamate Synthase (GLU1/GOGAT) involved in chloroplast nitrogen assimilation, as well as GUN4 and HEMA1 involved in chlorophyll biosynthesis. Overexpression and mutant lines of GNC maintained normal growth phenotypes outside of their differences in chlorophyll, chloroplast number and starch content. In contrast, expression of CGA1 also alters the developmental timing of Arabidopsis life cycle events, including flowering time and senescence. This work provides evidence that GNC and CGA1 have redundant roles in controlling chloroplast number and chlorophyll content based on environmental conditions including input from light and nitrate, while CGA1 is also involved in other cytokinin-related developmental functions. Transgenic rice (Oryza) plants with altered expression of the orthologs of GNC and CGA1 show similar phenotypes, including increased chlorophyll content. More importantly, preliminary analysis of these lines indicated that increased expression of GNC and CGA1 may increase biomass and yield under both nitrogen controlled conditions and at high density planting similar to conditions experienced in the field, which has important agricultural implications. |
