Characterization of an anther-expressed protein kinase gene in the potato Solanum berthaultii and its antisense inhibition in transgenic plants

Abstract

A cDNA clone (1.7 kb) isolated from a cDNA library of in-vitro germinated pollen from the potato species Solanum berthaultii contains an open reading frame of 465 amino acid residues. The predicted protein sequence has typical sequence characteristics of the catalytic subunit of the cyclic-nucleotide dependent protein kinases isolated from yeasts and animals, and the gene has been provisionally termed SBPK, (Solanum berthaultii protein kinase) A transcript of about 1.9 kb was detected on a northern blot in developing anthers, mature pollen, and in-vitro germinated pollen, but not in other plant tissues. The expression in anthers corresponds to the late uninucleate stage of microspore development. Isolation and nucleotide sequencing of a SBPK genomic clone revealed the kinase transcribed region to be interrupted by two introns, both close to the 5′end of the open reading frame, one upstream and one downstream of the start codon. Chimeric genes were constructed by fusing the coding sequence in the antisense orientation to the promoter of a strong late-expressed pollen gene, LAT52, and introduced in potato. Transformants fell into two classes, one displaying a typical antisense phenotype, and a second type arising from a cosuppression event. Both types of transformant gave rise to increased proportions of defective pollen, although the cosuppression effect was more severe. The results indicate that this anther-expressed protein kinase is essential for pollen development in potato.