Abstract
The phytohormone auxin transport and signaling are the key determinants of embryo patterning. To clarify the mechanisms underlying this process, we have analyzed the macchi-bou2 (mab2) mutant identified by a pinoid (pid) enhancer mutant screen. While pid single mutant seedlings showed only a mild phenotype in cotyledon number and/or positioning, the mab2 pid double mutant completely lacked cotyledons. The mab2 single mutant showed abnormal cell division during embryogenesis in addition to the abnormal cotyledon patterning. Using map-based cloning we identified the point mutation in the gene encoded a putative component of the Mediator complex, a general transcriptional regulator for RNA polymerase II, in mab2. MAB2 protein interacted with another mediator component in yeast, suggesting that MAB2 functions as the Mediator complex in Arabidopsis to regulate the transcription during embryogenesis.
