Cloning and phylogenetic analyses of serine/threonine kinase class defense-related genes in a wild fruit crop 'chestnut rose'

Serine/threonine kinase (STK) genes, encoding one of the important proteins for defense signal transduction, were cloned from 'chestnut rose'. Fifteen STK sequences were obtained by degenerate PCR. Sequence analysis showed that nine of them have continued open reading frames, and they are separated into five classes based on sequence analysis. Interestingly, one of the classes (STK V) showed less than 40% similarity to any other class, possibly representing new type genes from chestnut rose. Southern blotting analysis revealed that the new type STK V genes are single copy, while all the other genes have several copies in the genome. Phylogenetic analysis of STK genes from chestnut rose and 21 plant species revealed that most chestnut rose genes show close relationship with Rosaceae homologs, while the STK V genes are rather ancient and form a unique clade distantly from plant homologs.We cloned nine STK genes from a wild fruit crop 'chestnut rose', of which a new type of STK genes was identified. The new type STK genes exist as single copies in the genome, and they are phylogenetically distant to plant homologs. The polymorphic STK genes, combined with other plant immunity genes, provide plenty of resources to be utilized to defend against pathogens attack.Chestnut rose (Rosa roxburghii Tratt), a wild fruit crop in Southwest China, belongs to Rosaceae family Rosa genus. It has recently been labeled as one of the three promising new fruit crops in China due to its fruit having high content of vitamin C (2000-3000 mg/100 g FW), displaying high levels of superoxide dismutase (SOD) activity, and therefore is believed to have senescence-retarding and cancer-preventing effects [1]. Unfortunately, chestnut rose crops are suffering from powdery mildew disease. After decades of breeding, an indigenous cultivar from Guizhou province of China, Guinong No. 6, was discovered to be highly resistant to powdery mildew [2]. This material provides an opportunity to investigate the me