Characterisation of tomato MADS-box genes involved in flower and fruit development : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, New Zealand
MADS-box genes encode transcription factors that are involved in various aspects of plant development, by regulating target genes that control morphogenesis. Over the last decade, plant MADS-box genes have been studied extensively to reveal their control of floral development, especially in the model plants Arabidopsis and Antirrhinum. Their functions are however, not restricted to the flower but are involved in various aspects of plant development (Rounsley et al., 1995; Jack, 2001). By virtue of their extensive roles in the flower, these genes are expected to function in fruit development, which is a progression from flower morphogenesis. The aim of this study was to examine the role of MADS-box genes during flower and fruit development. Two new members of the tomato MADS-box gene family, TM10 and TM29 were identified. TM29 was isolated from a young fruit cDNA library by screening with homologous MADS-box fragments and TM10 was amplified by polymerase chain reaction from fruit cDNA templates. These genes were characterised by sequence and RNA expression patterns and their functions examined using molecular genetic techniques. Sequence analyses confirmed that both genes belong to the MADS-box family. TM29 shows 68% amino acid sequence identity to Arabidopsis SEP1 MADS-box protein. TM29 expression pattern showed similarities as well as differences to SEP1 (Flanagan and Ma. 1994). TM29 is expressed in shoot, inflorescence and floral meristems unlike SEP1, which is expressed exclusively in floral meristems (Flanagan and Ma. 1994). TM29 is expressed in all the four whorls of the flower. During floral organ development, it is highly expressed at early stages of the organ primordium but decreases as the organ differentiates and matures. In the mature flower bud, TM29 is expressed in the anther and ovary pericarp. During fruit development, TM29 is expressed from anthesis ovary to fruit of 14 days post-anthesis with its transcript localised to the pericarp and placenta. TM10 showed 64% amino acid identity to Arabidopsis AGL12. across the entire sequence. This notwithstanding, TM10 expression differed from AGL12. TM10 was expressed in shoot tissues of tomato and was not detected in roots. In contrast, the AGL12 gene transcript was only present in the roots of Arabidopsis (Rounsley et al., 1995). Expression was detected in leaves, shoot growing tips, floral buds and fruit. During fruit development, TM10 is expressed in anthesis ovary and in fruits at different growth stages. The functions of TM29 and TM10 were examined by transgenic techniques and phenotypes generated were consistent with their spatial and temporal gene expression patterns. TM29 transgenic phenotypes suggested it might be involved in the control of sympodial growth, transition to flowering, proper development of floral organs. parthenocarpic fruit development and maintenance of floral meristem identity. TM10 affected apical dominance and flowering time, development of floral organs and parthenocarpic fruit development.