Functional complementation of the Schizosaccharomyces pombe wis1 mutant byArabidopsis MEK1 and non-catalytic enhancement by CTR1

Arabidopsis thaliana MEK1 encodes a MAPKK homolog whose role in plants is c urrently unknown. High (hut not low) expression of MEK1 rescued the Delta w is1 (MAPKK) mutant of the Schizosaccharomyces pombe Win1/Wis4-Wis1-Sty1 str ess-activated MAPK pathway. Rescue was dependent upon upstream and downstre am components of the pathway, suggesting that MEK1 might function in a homo logous MAPK pathway in plants, When MEK1 was expressed at a low level, resc ue of Delta wis1 was achieved by co-expressing Arabidopsis CTR1 (a putative MAPKK kinase (MAPKKK)), CTR1 constructs alone did not rescue the pathway, indicating that CTR1 augmented MEK1 function, Further data indicated that t his enhancement was not due to CTR1 kinase activity. (C) 1999 Federation of European Biochemical Societies.