Comprehensive expression profiling analysis of OsIAA gene family in developmental processes and in response to phytohormone and stress treatments

Auxin is one of the most important phytohormones and exerts pleiotropic effects on plant growth and development. Aux/IAA and auxin response factor (ARF) are two important protein families that are well recognized for their roles in auxin-mediated responses. Aux/IAA proteins are short-lived transcriptional regulators that mediate auxin responses through interaction with ARF transcription factors. Here, we systematically compared the genomic organization of the two families in rice. The expression profiles of both families were compared to show possible association of the two gene families at expression level, which would help reveal their synergistic relationships and functions. The expression profile analysis of Aux/IAA and ARF genes in 30 organs/tissues (collected from an entire life cycle of rice) suggested that Aux/IAA and ARF genes are expressed in very diverse patterns. In general, the genes showing similar expression patterns tended to be in the same phylogenetic subgroup even though their expression patterns were not always the same. Hierarchical cluster analysis revealed that there are eight pairs of IAA and ARF genes, with each pair showing highly correlated expression. The expression levels of the IAA gene family were also checked under various hormone treatments including abscisic acid, kinetin, gibberellin, jasmonic acid, auxin and brassinolide. The results indicated that most of the IAA genes respond to at least one of the treatments. Furthermore, DNA chip and real-time PCR results show that many genes in these families were responsive to various abiotic stresses, indicating an interaction between plant growth and abiotic stress. The effect of abiotic stress on plant growth and auxin distribution was further confirmed with the root growth of DR5-GUS transgenic rice under mannitol treatment, in which a close association between mannitol-induced changes of auxin distribution and root growth was observed.