Gene expression, localization, and protein–protein interaction of Arabidopsis SKP1-like (ASK) 20A and 20B

Arabidopsis SKP1-like 20 (ASK20) has two translational products, ASK20A and ASK20B, as a result of alternative splicing. Both ASK20A and ASK20B mRNAs were detected in every organ examined, and only small differences in their accumulation levels were observed in plants exposed to abiotic stress or treated with growth regulators. Transgenic plants possessing ASK20 promoter:GUS (β-glucuronidase) displayed GUS activity in the root, leaf, flower, and seed, in agreement with reverse transcriptase-polymerase chain reaction (RT-PCR) results. Transgenic plants possessing ASK20 promoter:ASK20B-GUS showed a pattern of GUS activity similar to that of ASK20 promoter:GUS plants, whereas transgenic plants possessing ASK20 promoter:ASK20A-GUS displayed little GUS activity in the root vein, cotyledon, sepal, and stamen. GUS activity of the transiently expressed ASK20A-GUS and ASK20B-GUS as well as green fluorescent protein (GFP) signals for ASK20A-GFP and ASK20B-GFP in transgenic plants were localized in the cytosol. In a yeast two-hybrid system, both ASK20A and ASK20B interacted with two F-box proteins (At3g61590 and At5g39250). Neither ASK20A nor ASK20B interacted with CUL1 (cullin1) in the yeast two- or three-hybrid system, and little interaction of ASK20 proteins with CUL1 was detected in a pull-down assay.