Genetic analysis of DEK1 loop function in three-dimensional body patterning in physcomitrella patens.

DEK1 of higher plants plays an essential role in position dependent signaling and consists of a large transmembrane domain (MEM) linked to a protease catalytic domain (CysPc) and a regulatory domain (C2L). Here we show that the postulated sensory Loop of the MEM domain plays an important role in the developmental regulation of DEK1 activity in the moss Physcomitrella patens. Compared with P. patens lacking DEK1 (∆dek1), the dek1∆loop mutant correctly positions the division plane in the bud apical cell. In contrast to an early developmental arrest of ∆dek1 buds, dek1∆loop develops aberrant gametophores lacking expanded phyllids resulting from mis-regulation of mitotic activity. In contrast to the highly conserved sequence of the catalytic CysPc domain, the Loop is highly variable in land plants. Functionally, the sequence from Marchantia polymorpha fully complements the dek1∆loop phenotype, whereas sequences from Zea mays and Arabidopsis thaliana give phenotypes with retarded growth and affected phyllid development. New bioinformatic analysis identifies MEM as a member of the Major Facilitator Superfamily, membrane transporters reacting to stimuli from the external environment. Transcriptome analysis comparing WT and ∆dek1 tissues identifies an effect of two groups of transcripts connected to dek1 mutant phenotypes, i.e. transcripts related to cell wall remodeling and regulation of the APB2 and APB3 transcription factors known to regulate bud initiation. Finally, new sequence data support the hypothesis that the advanced charophyte algae that evolved into ancestral land plants lost cytosolic calpains, retaining DEK1 as the sole calpain in the evolving land plant lineage