Functional Analysis Of MADS-box Genes In Monocot Flower Development

MADS-box genes encode a family of transcriptional factors that play a key role in flower development. Studies on several floral homeotic mutants in dicots, mainly in Arabidopsis, Snapdragan and Petunia, established the ABCDE model for the determination of floral organ identities. Class E genes contribute to the development of petals, stamens and carpels, in addition to sepals. It also specifies the floral meristem identity. In grasses, E-function genes underwent a relatively rapid functional diversification. There are at least five class E genes in rice. They are OsMADS1, OsMADS5, OsMADS7 (OsMADS45), OsMADS8 (OsMADS24) and OsMADS34, in which OsMADS1 is currently the best characterized, the others are not documented well. On the basis of the results from dicots, we investigated the E function genes in rice using In Situ Hybridization and RNAi technique. The results showed that OsMADS8/7 transcripts are first detected in branching primordia, then in spikelet meristem primordia. With the development of the flower, OsMADS8 transcripts are localized in the lodicules, developing stamens and pistil. OsMADS8 continues to express in integuments, developing embryo and endersperm. OsMADS5 has similar expression patterns to OsMADS8/7. The difference is that OsMADS5 transcripts present in all floral whorls at early stage of the flower development. Silencing of OsMADS8 by RNAi strategy had no phenotypic alteration when compared to wild-type plants, but if all the E function genes were silenced in the mean time, the floral organs and heading date were seriously affected. The palea and lemma were transformed into leaf-like structures; the lodicules were palea-like and the stamens did not produce pollen. The carpels had characteristics of palea/lemma. Ovule was not formed in the aberrant carpel and floral reversion occurred. It suggested that there is functional redundancy among class E genes in rice, in addition to the diversification; class E genes are required for the development of all four floral organs and ovule; E function genes specify the floral meristem identity and affected the heading date of rice. Studies on the regulatory sequence of MADS-box genes will reveal spatial and temporal control of gene expression. ZAG2 gene belongs to the class D gene of MADS-box genes in maize. It expresses in ovules and carpels. We isolated the sequence of 3040bp upstream of the translational start site of the gene. The transcriptional start site in the sequence was identified by the method of 5'-RACE. Two gene fusions between the ZAG2 genomic region and the GUS reporter gene were assembled and introduced into rice. We analyzed the regulatory sequence according to the primary results.