CHARACTERIZATION OF BP-HOX, AN ALTERNATIVE SPLICING ISOFORM OF THE ARABIDOPSIS KNAT1/BP TRANSCRIPTION FACTOR THAT LACKS THE PROTEIN-PROTEIN INTERACTION DOMAIN

Knotted1-like homeobox (KNOX) transcription factors belong to the three amino acid loop extension (TALE) superclass of homeodomain proteins in higher plants (Hay and Tsiantis, 2010; Hamant and Pautot, 2010; Wu and Smith 2012; Di Giacomo et al., 2013). KNOX1 proteins play a key role in several developmental processes by maintaining a proper balance between undifferentiated and differentiated cell state through the modulation of multiple hormonal pathways Besides the homeodomain, KNOX proteins are characterized by the presence of a consensus region called MEINOX that defines this subclass of the TALE family. MEINOX domain is important for protein-protein interactions with a second group of TALE proteins, the BEL-like homeodomain (BLH) family. This interaction modulates KNOX nuclear localization and, likely, target selection . Mutations in KNAT1/BREVIPEDICELLUS (KNAT1/BP), one of the four Arabidopsis KNOX1 genes, result in plants with shorter internodes, downward pointing siliques, altered intra-bundle cell identity and altered lignin deposition (Mele et al., 2004). Recently, KNATM, a novel Arabidopsis KNOX1 gene that encodes a MEINOX domain but lacks the homeodomain was identified and shown to regulate KNAT1/BP (Magnani and Hake, 2008). We identified and characterized a novel isoform of KNAT1/BP transcription factor that arises from an event of alternative splicing and may encode a novel protein (BPhox) that contains the homeodomain but lacks the MEINOX domain. Phenotype and molecular analysis of Arabidopsis lines that overexpress each isoforms under the control of constitutive/inducible promoters and complementation analyses were carried out to unravel the function of BPhox in inflorescence architecture, vascular development and lignin deposition.