Phylogenetic analysis of the AP2/ERF and KNOTTED1-like homeodomain families of transcription factors and finding of new members in Zea mais and Arabidopsis thaliana

The AP2/ERF is one of the most represented families of transcription factors in plants with 144 AP2/ERF genes predicted in the Arabidopsis thaliana genome. All members of the AP2/ERF family of plant transcription regulators contain at least one copy of a DNA-binding domain called the AP2 domain. The AP2 domain was considered plant unique. In this study, I show that homologs of the AP2 domain are present outside plants. The newly discovered non-plant proteins bearing an AP2 domain are predicted to be HNH endonucleases. I hypothesize that a horizontal transfer of an HNH-AP2 endonuclease from bacteria or viruses into plants may have led to the origin of the AP2/ERF family of transcription factors via transposition and homing processes.;Some members of the AP2/ERF family of transcription factors are involved in key developmental steps. BRANCHED SILKLESS 1 (BD1), a putative ERF transcription factor, plays a fundamental role in the maize spikelet development controlling meristem identity. I took a reverse genetic approach in order to clone new AP2/ERF factors involved in the development of the maize inflorescence architecture. I cloned four genes that are specifically expressed in ear and tassel. All of them are down-regulated in the bd1 background. The ongoing analysis of the Mu insertion mutant alleles that have been found for all the four ERF genes will help understand the role of these transcription factors.;The KNOTTED1-like homeodomain (KNOX) family of transcription regulators is the second protein family I focused my attention on. KNOXs are Three Amino acid Loop Extension (TALE) homeodomain proteins. KNOXs also carry a MEINOX domain which interacts with the TALE BEL1-like homeodomain proteins. In this study, I analyze the phylogeny of the Arabidopsis KNOX proteins and identify MNX, a new Arabidopsis KNOX which encodes a MEINOX domain and an acidic domain, but no homeodomain. As predicted, MNX selectively interacts with BELL proteins. MNX is expressed in a polar way in organ primordia. pCaMV35S:MNX Arabidopsis plants show defects in petiole elongation, leaf serration and flowering time. Taken together the data suggest that MNX-B work as a typical KNOX transcription factor with the homeodomain being redundant.