Characterization of the Arabidopsis MADS-box transcription factor, AGL104 : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand
AGL104 is an Arabidopsis MADS-box transcription factor belonging to the MIKC* clade. The exclusive expression of MIKC* genes in the gametophyte generation of both mosses and angiosperms has fueled questions regarding the function of these genes in both these taxa and the notion that the developmental program of the gametophyte generation in both these taxa may be fundamentally similar even though the structures themselves differ greatly in their phenotype. Since transcription factors control development and changes in the developmental control genes is thought to be a major source of evolutionary changes in morphology, characterization of MIKC* genes is expected to provide clues to the evolutionary changes in land plant body form. In angiosperms. AGL104 is reported to be expressed late and exclusively in the male (pollen) and female (embryo sac) gametophyte. Since late pollen development, such as pollen germination and pollen tube elongation, is thought to occur independently of transcription, the exclusive and high level of expression of a transcription factor is thus intriguing. We report the expression of AGL104 in developing anthers, mature pollen, pollen tubes and the egg apparatus of the embryo sac. Our study is the first report of AGL104 expression in the pollen tubes. Our data showing spatial expression of AGL104 in the different developmental stages of pollen, with weak expression in the uninucleate microspore that increases and culminates in the mature pollen, is also novel since spatial expression of this gene during pollen development had not been previously reported. Functional characterization through gain-of-function and loss-of-function analyses shows that AGL104 promotes pollen germination and an increased pollen tube length when measured 4 hours after pollination. The implication of this data is that, despite popular notions, active gene regulation is taking place during pollen germination and tube elongation. Further functional analysis in the pollen and the embryo sac is required to establish the precise role of AGL104 in the angiosperms. This information will then lay the groundwork for future comparisons of MIKC* activity in the basal and higher plants and determine if changes in MIKC* gene function were responsible for evolutionary changes in land plant body form.