A differentially expressed bZIP gene is associated with adventitious shoot regeneration in leaf cultures of Paulownia kawakamii

Abstract

Plant regeneration in tissue culture is important for the successful application of transgenic technology in crop improvement. We isolated a bZIP motif containing cDNA (PKSF1) from excised leaf cultures of the fast-growing tree Paulownia kawakamii by a novel subtractive hybridization strategy. PKSF1 codes for a leucine zipper transcription factor and is preferentially expressed during adventitious shoot regeneration. It showed about a sixfold higher level of expression in the shoot-forming tissues compared to the callus-forming cultures of Paulownia. In situ hybridization analysis showed that PKSF1 expression was localized in the developing shoot primordia of the shoot-forming cultures. It was also expressed in the apical meristem and provascular tissues in the vegetative shoot apex. Quantitative polymerase chain reaction results showed that only basal levels of transcripts were present in callus-forming tissues at day 0 and day 10, whereas maximal expression was seen in shoot-forming tissues at day 10, suggesting that PKSF1 is associated with adventitious shoot bud development in Paulownia.