Poster: Photomorphogenesis

Abs # 515: A cyclic nucleotide-gated, calmodulin-binding potassium channel involved in photomorphogenic processes in Arabidopsis thaliana

Presenter:	Borsics, Tamas , borsics@abc.hu
Authors	Borsics, Tamas  (A)   Li, Xinli  (A)   Harrington, Michael  (A)   Wu, Chengxiang  (A)   Christopher, David A (A)
Affiliations:	(A): University of Hawaii

We have isolated and characterized a new member of the family of inward rectifying K+ channels, designated ACBK1, from Arabidopsis thaliana. ACBK1 is homologous to the Shaker-type superfamily and the cyclic nucleotide-gated and calmodulin (CaM)-regulated K+ channels. ACBK1 has six membrane spanning domains, a pore domain and a putative cNMP-binding domain that overlaps a CaM-binding domain located at the C-terminus. CaM-gel overlay analysis revealed ACBK1 is a CaM-binding protein and forms a typical basic amphiphilic structure. Complementation tests in K+ channel mutants of E. coli, yeast and Arabidopsis confirm ACBK1 is a K+ channel. Although ACBK1 is not a highly selective ion channel in bacteria, it is highly selective in yeast. Biochemical analysis revealed Ca2+/CaM inhibited K+ uptake, while cGMP reversed this inhibition in E. coli. Relative to wild type, the antisense ACBK1 plants flowered 12-18 days earlier, had a 30% reduction in leaf thickness, altered chloroplast mRNA levels, and chloroplasts with aberrant starch accumulation at higher light fluences. The results suggest a role for ACBK1 in K+ balance involved in developmental and photomorphogenic processes.