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

Author(s): W. Zhai, Y. Zhao, L.X. Zhang and X.J. Li

The tomato Pto gene encodes a serine/threonine kinase (STK) whose molecular characterization has provided valuable insights into the disease resistance mechanism of tomato. Therefore, Pto 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 a hevea cultivar (Hevea brasiliensis Muell. Arg). A fragment of ~550 bp was amplified, cloned, and sequenced. The sequence analysis of several clones revealed 12 distinct sequences highly similar to STKs. Based on their significant similarity with the tomato Pto protein (BLASTX E value < 3e-53), seven sequences were classified as Pto resistance gene candidates (Pto-RGCs). Multiple sequence alignment of the hevea Pto-RGC products revealed that these sequences contain several conserved subdomains present in most STKs, as well as several conserved residues that are crucial for Pto function. Moreover, phylogenetic analysis showed that the hevea Pto-RGCs clustered with Pto, suggesting a common evolutionary origin with this resistance gene. The Pto-RGCs isolated in this study represent a valuable sequence resource that could assist in the development of disease resistance in hevea.