Structure and expression analysis of three subtypes of Arabidopsis MBF1 genes.

Multiprotein bridging factor 1 (MBF1) is a transcriptional co-activator that mediates transcriptional activation by bridging between an activator and a TATA-box binding protein (TBP). Recently, we have reported that three Arabidopsis MBF1s play roles as transcriptional co-activators. This study shows that AtMBF1c is totally different from the other two in its structure and expression pattern, and that MBF1c genes also occur in other plant species, including monocots. We performed histochemical analysis of these genes using beta-glucuronidase (GUS) assays to characterize the expression profile of each AtMBF1 gene extensively. In pAtMBF1a Colon, two colons GUS transformants, GUS staining was observed only in anthers and seeds, whereas strong GUS activity in pAtMBF1b Colon, two colons GUS transformants was detected in leaf veins, stems, anthers, and seeds. In mature pAtMBF1c Colon, two colons GUS transformants, GUS staining was observed in almost all tissues. It is noteworthy that intense GUS staining was observed in anthers of all transformants. We also found that AtMBF1c expression was up-regulated upon diverse stress treatments including exposure to heat, hydrogen peroxide, dehydration, and high concentrations of salt. These findings suggest that AtMBF1c may be involved in stress response pathway.