1). Viktor Demko, Pierre-François Perroud, Wenche Johansen, Charles F. Delwiche, Endymion D. Cooper, Pål Remme, Ako Eugene Ako, Karl G. Kugler, Klaus F.X. Mayer, Ralph Quatrano, and Odd-Arne Olsen* (2014). Genetic Analysis of DEK1 Loop Function in Three-Dimensional Body Patterning in Physcomitrella patens. Plant Physiology 166:903-919 http:/ / dx. doi. org/ 10. 1104/ pp. 114. 243758
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.
2). Pierre-François Perroud, Viktor Demko, Wenche Johansen, Robert C. Wilson, Odd-Arne Olsen, and Ralph S. * (2014). Defective Kernel 1 (DEK1) is required for three-dimensional growth in Physcomitrella patens. New Phytologist 203: 794-804.
- Orientation of cell division is critical for plant morphogenesis. This is evident in the formation and function of meristems and for morphogenetic transitions. Mosses undergo such transitions: from two-dimensional tip-growing filaments (protonema) to the generation of three-dimensional leaf-like structures (gametophores).
- The Defective Kernel 1 (DEK1) protein plays a key role in the perception of and/or response to positional cues that specify the formation and function of the epidermal layer in developing seeds of flowering plants. The moss Physcomitrella patens contains the highly conserved DEK1 gene.
- Using efficient gene targeting, we generated a precise PpDEK1 deletion (∆dek1), which resulted in normal filamentous growth of protonema. Two distinct mutant phenotypes were observed: an excess of buds on the protonema, and abnormal cell divisions in the emerging buds resulting in developmental arrest and the absence of three-dimensional growth. Overexpression of a complete PpDEK1 cDNA, or the calpain domain of PpDEK1 alone, successfully complements both phenotypes
- These results in P. patens demonstrate the morphogenetic importance of the DEK1 protein in the control of oriented cell divisions. As it is not for protonema, it will allow dissection of the structure/function relationships of the different domains of DEK1 using gene targeting in null mutant background.
3). Khandelwal, A., Cho, S. H., Marella, H., Sakata, Y., Perroud, P-F., Pan, A., and Quatrano, R. S. (2010). Role of ABA and ABI3 in desiccation tolerance. Science 327: 546.
To survive on land, the earliest land plants had to develop mechanisms to tolerate desiccation. Modern vascular plants possess an array of morphological features to retain water (such as conductive tissues, cuticle, and stomata) and have retained desiccation tolerance in only a few specialized structures (e.g., seeds). Present-day bryophytes (mosses), in contrast, lack water transport and retention tissues, presumably like early land plants. As a result, their vegetative state is at equilibrium with the surrounding air, creating a water-deficit condition that most angiosperms could not tolerate (1). Phylogenetic analyses suggest that desiccation tolerance in vegetative tissue of bryophytes was lost in the first vascular plants (2). Here, we evaluate whether desiccation tolerance in angiosperm seeds and in vegetative tissues of the moss Physcomitrella patens use similar regulatory pathways. We conclude that both ABA and ABI3 are required for P. patens vegetative tissue to survive desiccation. Because the P. patens genome lacks the transcription factors FUS3 and LEC2 that are required for seed maturation like ABI3, the role of ABI3 in this non-seed plant appears to be directly in desiccation tolerance, primarily in the recovery stage. Our working hypothesis is that gene regulatory pathways that include both ABA and ABI3 originally evolved for cellular protection from water deficits but independently have been used to provide desiccation tolerance in vegetative tissues of bryophytes and in angiosperm seeds.