Abstract
Brassinosteroids (BR) affect a range of developmental characteristics, including hypocotyl and pollen tube elongation, flowering time and germination. Proteins involved in biosynthesis and in signaling have been identified through loss-of-function mutants, while enzymes of BR metabolism have been found by screening of overexpression lines.
Searching the Arabidopsis FOX collection for altered organ size, we identified PIZZA. The PIZZA overexpression line strongly resembles BR deficient plants. This phenotype could be rescued by supply of exogenous brassinolide and castasterone. The expression of PIZZA due to promotor-GUS reporter lines seems to be specific to root and floral tissues. Based on the complementation phenotype and sequence analysis, we suggest a role for PIZZA in BR metabolism rather than biosynthesis. As PIZZA knock out lines show no developmental phenotype, redundant enzymes are likely to exist. We are currently investigating the in vitro and in vivo function of the PIZZA protein, especially in comparison to the known P450 hydroxylases BAS1 and SOB7. Preliminary data from double mutant analysis also indicates a role of PIZZA in the inhibition of organ elongation.
