Over-expression of a flower-specific transcription factor gene AtMYB24 causes aberrant anther development

In plants, MYB transcription factors play important roles in many developmental processes and various defense responses. AtMYB24, as a member of R2R3-MYB gene family in Arabidopsis, was found mainly expressed in flowers, especially in microspores and ovules using Northern blots and in situ hybridization. It was further found that the expression of AtMYB24 was tightly regulated during anther development. Over-expression of AtMYB24 in transgenic plants resulted in pleiotropic phenotypes, including dwarfism and flower development defects, in particular, producing abnormal pollen grains and non-dehiscence anthers. Further analysis showed that the anther development of the AtMYB24-ox lines was retarded starting from the anther developmental stages 10-11. At stages 12 and 13, the septum and stomium cells of anthers would not break, and fewer or no fibrous bands were found in the endothecium and connective cells in the AtMYB24-ox plants. Similar aberrant anther phenotype was also observed in the AtMYB24-GR-ox lines treated with dexamethasone (DEX). Quantitative real-time PCR showed expression of genes involved in phenylpropanoid biosynthetic pathway, such as CHS and DFR, and AtGTP2 were altered in AtMYB24-ox lines. These results suggest an important role of AtMYB24 in the normal development of anthers in Arabidopsis.