Isolation, characterization and expression studies of resistance gene candidates (RGCs) from Zingiber spp.

Ginger (Zingiber officinale Rosc.) production is seriously affected by many fungal and bacterial diseases to which no resistant source is available in the cultivated germplasm. Degenerate primers based on conserved motifs of plant resistance (R) genes were used to isolate analogous sequences called resistance gene candidates (RGCs) from cultivated and wild Zingiber species. Cloning and sequence characterization identified 42 Zingiber RGCs, which could be classified into five classes following phenetic analysis. Deduced amino acid sequences of Zingiber RGCs showed strong identity, ranging from 16 to 43%, to non-toll interleukin receptor (non-TIR) R-gene subfamily. Non-synonymous to synonymous nucleotide substitution (dN/dS) ratio for the NBS domains of Zingiber RGC classes showed evidence of purifying selection. RT-PCR analysis with 15 Zingiber RGC-specific primers demonstrated 8 of the 15 Zingiber RGCs to be expressed. The present study reports for the first time the isolation and characterization of RGCs from ginger and its wild relatives, which will serve as a potential resource for future improvement of this important vegetatively propagated spice crop.