Structural and phylogenetic analysis of Pto-type disease resistance gene candidates in banana

The tomato Pto gene encodes a serine/threonine kinase (STK) whose molecular characterization has provided valuable insights into the disease resistance mechanism of tomato and it is considered as a promising candidate for engineering broad-spectrum pathogen resistance in this crop. In this study, a pair of degenerate primers based on conserved subdomains of plant STKs similar to the tomato Pto protein was used to amplify similar sequences in banana. A fragment of ∼550 bp was amplified, cloned and sequenced. The sequence analysis of several clones revealed 13 distinct sequences highly similar to STKs. Based on their significant similarity with the tomato Pto protein (BLASTX E value <3e-53), seven of them were classified as Pto resistance gene candidates (Pto-RGCs). Multiple sequence alignment of the banana Pto-RGC products revealed that these sequences contain several conserved subdomains present in most STKs and also several conserved residues that are crucial for Pto function. Moreover, the phylogenetic analysis showed that the banana Pto-RGCs were clustered with Pto suggesting a common evolutionary origin with this R gene. The Pto-RGCs isolated in this study represent a valuable sequence resource that could assist in the development of disease resistance in banana.