Poster: Photomorphogenesis

Abs # 390: A cyclic nucleotide-regulated, calmodulin-binding potassium channel is involved in several developmental processes in Arabidopsis thaliana

Presenter:	Borsics, Tamas , borsics@hawaii.edu
Authors	Borsics, Tamas  (A)   Li, Xinli  (A)   Harrington, Michael  (A)   Webb, David  (A)   Christopher, David A (A)
Affiliations:	(A): University of Hawaii at Manoa, Honolulu

Potassium is a major macronutrient and the most abundant cation in plants. K⁺ is required for normal growth, photosynthesis, tropisms, cell expansion, enzyme homeostasis, stomatal opening and osmeregulation. A variety of K⁺ transporters are responsible for accumulation of K⁺ from soil and its distribution throughout the plant. We have isolated and characterized a new member of the calmodulin (CaM)-regulated, cyclic nucleotide-gated channel family, designated CNGC10, from Arabidopsis thaliana. CNGC10 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. The CaM-binding domain was mapped via CaM-gel overlay experiments. Complementation tests in K⁺ channel uptake defective mutants of E. coli (LB650), yeast (CY162) and Arabidopsis (akt1-1) proved that CNGC10 is an inward conducting K⁺ channel. In E. coli Ca²⁺/CaM inhibited K⁺ uptake, while cGMP reversed this inhibition. Ca²⁺ alone did not effect channel activity. The antisense plants had a low level of CNGC10 mRNA and protein was undetected with a CNGC10-specific antibody. However, the mRNA levels of the most closely homologous channel, CNGC13, were not reduced in antisense CNGC10 plants indicating the antisense effect is specific to CNGC10. Antisense plants flowered 12-18 days earlier relative to wild type, had a 30% reduction in leaf thickness and mesophyll cell size, high levels of starch in chloroplasts and slower gravity responses. They also contain 40% less potassium in the leaves than wild type plants. We propose a role for CNGC10 in regulating K⁺ balance involved in several developmental processes.