Isolation and Characterisation of PRSV-P Resistance Genes inCaricaandVasconcellea

Papaya (Carica papayaL.) is one of the major tropical fruit crops worldwide, but it is limited throughout its range by papaya ringspot virus type P (PRSV-P). Previous genetic studies identified a functional PRSV-P resistance marker in a mapping population of F2plants ofVasconcellea pubescens(resistant to PRSV-P) ×Vasconcellea parviflora(susceptible to PRSV-P) and showed that the marker exhibited homology to a serine threonine protein kinase (STK) gene. Full length cDNAs of putative PRSV-P resistance genes designated CP_STK fromC. papayaand VP_STK1 and VP_STK2 fromV. pubescenswere cloned by rapid amplification of cDNA ends (RACE). Due to a frame-shift mutation, the two homologous sequences are transcribed and edited differently such that the gene product inV. pubescensis two separate transcripts, whereas inC. papayathey are fused into a single message. A peroxisomal targeting signal (PTS2) present in VP_STK2 but absent in the other transcripts may be the functional source of PRSV resistance inV. pubescens. The STK gene fromV. pubescensmay have been derived from an alternative splicing to confer resistance. The putative resistance gene,VP_STK2, that was identified in this study is a potential new source of PRSV-P resistance for papaya genotypes.