TaWAK6 encoding wall-associated kinase is involved in wheat resistance to leaf rust similar to adult plant resistance

Abstract

In wheat, adult plant resistance (APR) to leaf rust (Puccinia triticina), is effective in restricting pathogen growth and provides durable resistance against a wide range of virulent forms of P. triticina. Despite the importance, there is limited knowledge on the molecular basis of this type of resistance. We isolated and characterized the wall-associated kinase encoding gene in wheat, and assigned it as TaWAK6. Localization of TaWAK6 homeologs in A and B wheat subgenomes was consistent with the presence of the gene’s orthologs in T. urartu (AA) and T. dicoccoides (AABB) and with the absence of its orthologs in Aegilops tauschii (DD). Overexpression of TaWAK6 did not change the wheat phenotype, nor did it affect seedling resistance. However, the adult plants overexpressing TaWAK6 showed that important parameters of APR were significantly elevated. Infection types scored on the first (flag), second and third leaves indicated elevated resistance, which significantly correlated with expression of TaWAK6. Analysis of plant-pathogen interactions showed a lower number of uredinia and higher rates of necrosis at the infection sites and this was associated with smaller size of uredinia and a longer latent period. The results indicated a role of TaWAK6 in quantitative partial resistance similar to APR in wheat. It is proposed that TaWAK6, which is a non-arginine-aspartate (non-RD) kinase, represents a novel class of quantitative immune receptors in monocots.