Transmembrane-anchored DEK1 calpain is a key determinant of the plant epidermis - also a key to the development of differentiated multicellular land plants?
Friday seminar by Odd-Arne Olsen
Dek1 (Defective kernel 1) from maize encodes an atypical calpain consisting of the fusion of a 21 transmembrane anchor and a calpain with conserved domains I, II, III. The gene was identified and cloned in maize, where the homozygous mutant seeds lack the aleurone layer, one of the major seed tissues. Subsequently, it was shown that DEK1 is a key regulator of epidermal cell development in all plant tissues in most, if not all plants. Unlike other groups of organisms, Angiosperms have only one calpain, that in the Dek1 gene. Recent data suggest that the event creating the DEK1 gene occurred an estimated 800 million years ago, being present in the unicellular Charophyte green alga Mesostigma viride and representative species in the land plant lineage up to higher land plants (angiosperms). In contrast, the unicellular Chlorophyte green alga Chlamydomonas reinhardtii has four calpain genes. Our hypothesis is that DEK1 was fundamental to regulating the expansion of the primitive two-dimensional plant body to three dimensional land plants which evolved to conquer land. We are currently pursuing investigations to identify the role of calpains and DEK1 in the land plant lineage using knock-down and knock-out technology in representative species of the land plant lineage, including Chlamydomonas reinhardtii and the moss Physcomitrella patens. In addition, cloning and expression of different domains of Arabidopsis thaliana DEK1 are in progress for structural and functional studies.
Norwegian University for Life Sciences, Aas, Norway; & Hedmark University College