A cAMP‐Dependent Protein Kinase Gene,aapk1, Is Required for Mycelia Growth,Toxicity and Pathogenicity of Alternaria alternata on Tobacco

The fungus Alternaria alternata is a common spot‐producing plant pathogen. During the past decade, tobacco brown spot disease caused by this fungus has became prevalent in China and lead to significant losses. To better understand the molecular pathogenesis of this fungus, the aapk1 gene encoding a cAMP‐dependent protein kinase catalytic subunit was cloned, sequenced and characterized. The aapk1 deletion mutants were identified from hygromycin‐resistant transformants by PCR strategy and confirmed by Southern blot analysis and RT‐PCR. The aapk1 deletion mutant exhibited reduced vegetative growth and was less toxic than the wild‐type strain sd1. Deletion of aapk1 also delayed disease development on detached tobacco leaves. Thus, we propose that the cAMP signalling pathway is involved in mycelia growth and pathogenic phenotype of Alternaria alternata.