Abstract
BackgroundPowdery mildew, caused by Blumeria graminearum f.sp. tritici (Bgt), is one of the most severe fungal diseases of wheat. The exploration and utilization of new gene resources is the most effective approach for the powdery mildew control.ResultsWe report the cloning and functional analysis of two wheat LRR-RLKs from T. aestivum c.v. Prins- T. timopheevii introgression line IGV1-465, named TaRLK1 and TaRLK2, which play positive roles in regulating powdery mildew resistance in wheat. The two LRR-RLKs contain an ORF of 3,045 nucleotides, encoding a peptide of 1014 amino acids, with seven amino acids difference. Their predicted proteins possess a signal peptide, several LRRs, a trans-membrane domain, and a Ser/Thr protein kinase domain. In response to Bgt infection, the TaRLK1/2 expression is up-regulated in a developmental-stage-dependent manner. Single-cell transient over-expression and gene-silencing assays indicate that both genes positively regulate the resistance to mixed Bgt inoculums. Transgenic lines over-expressing TaRLK1 or TaRLK2 in a moderate powdery mildew susceptible wheat variety Yangmai 158 led to significantly enhanced powdery mildew resistance. Exogenous applied salicylic acid (SA) or hydrogen peroxide (H2O2) induced the expression of both genes, and H2O2 had a higher accumulation at the Bgt penetration sites in RLK over-expression transgenic plants, suggesting a possible involvement of SA and altered ROS homeostasis in the defense response to Bgt infection. The two LRR-RLKs are located in the long arm of wheat chromosome 2B, in which the powdery mildew resistance gene Pm6 is located, but in different regions.ConclusionsTwo members of TaRLK family were cloned from IGV1-465. TaRLK1 and TaRLK2 contribute to powdery mildew resistance of wheat, providing new resistance gene resources for wheat breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0713-8) contains supplementary material, which is available to authorized users.
Highlights
Powdery mildew, caused by Blumeria graminearum f.sp. tritici (Bgt), is one of the most severe fungal diseases of wheat
Cloning and sequence analysis of TaRLK1 and TaRLK2 Previous study suggested that a cluster of LRR-Receptor-like kinase (RLK) genes located in the long arm of chromosome 2B of T. aestivum -T. timopheevii introgression line IGV1-465
Our analyses revealed that, compared with the 60.41 % Haustorium Index (HI) in Prins transformed with pAHC25 only, transient overexpression of TaRLK1 or TaRLK2 in leaves of Prins by co-transformation of pBI220:TaRLK1 or pBI220:TaRLK2 with pAHC25 significantly decreased the HI to 53.72 % and 37.55 %, respectively
Summary
Powdery mildew, caused by Blumeria graminearum f.sp. tritici (Bgt), is one of the most severe fungal diseases of wheat. Receptor-like kinase (RLK) membrane proteins serve as pattern recognition receptors (PRRs) and play essential roles in detecting pathogen-associated molecular patterns (PAMPs). They initiates basal and broad-spectrum defense, known as. The rice gene Xa21, which codes for an LRRRLK with extracellular LRR repeats of amino acids each and an intracellular serine/threonine kinase domain, confers race-specific resistance to Xoo (Xanthomonas oryzae pv oryzae) [4]. Xa21 is developmentally controlled: juvenile rice plants challenged with Xoo are less resistant than older plants [5]. Xa3/Xa26 encodes an LRRRLK, but does not appear to be developmentally regulated, as both juvenile and adult plants exhibit resistance against Xoo [6]. Only a few RLKs have been functionally identified, which is even more so in common wheat (Triticum aestivum L.)
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