Generation of the domneg-1 and kincless Mutants. Site-directed mutagenesis was performed on the KAT2 cDNA to replace the selectivity filter GlyTyrGlyAsp motif (hallmark of K⁺-selective channels) by ArgArgGlyAsp. The mutated cDNA, named domneg, was cloned downstream of the KAT2 promoter region (2.258 kb upstream from the initiation codon) into a binary vector (pBIB-HYGRO), and the resulting plasmid was introduced into Agrobacterium tumefaciens GV3010 (pMP90) strain as described (10). WT plants (Wassilevskija ecotype) and kat2-1 mutant plants were transformed by using the floral dip method (27). Selection on hygromycin allowed us to identify transformed lines and to obtain a fixed transgenic domneg-1 or kincless line, respectively.