Pattern recognition receptors (PRRs) can trigger plant immunity through the recognition of pathogen-associated molecular patterns. In this study, we report that a malectin-like/leucine-rich repeat receptor protein kinase gene, RLK-V, from Haynaldia villosa putatively acts as a PRR to positively regulate powdery mildew resistance caused by Blumeria graminis f. sp. tritici (Bgt) in wheat. RLK-V has two alternatively spliced transcripts corresponding to an intact RLK-V1.1 and a truncated RLK-V1.2 caused by intron retention. Expression analysis showed that both transcripts could be up-regulated by Bgt in resistant materials, whereas the functional RLK-V1.1 was expressed only after Bgt inoculation. Promoter activity assays indicated that RLK-V could respond to Bgt even in susceptible wheat. Silencing of RLK-V in Pm21-carrying resistant materials resulted in compromised resistance to Bgt. In addition, over-expression of RLK-V1.1 in Pm21-lacking susceptible Yangmai158 and SM-1 by single-cell transient expression and stable transformation in Yangmai158 could improve powdery mildew resistance. We propose that RLK-V regulates basal resistance to powdery mildew, which is also required for broad-spectrum resistance mediated by the Pm21 gene. Over-expression of RLK-V1.1 could trigger cell death in Nicotiana benthamiana, and RLK-V1.1 transgenic wheat accumulated more reactive oxygen species and displayed a stronger hypersensitive response than did the recipient, which led to enhanced Bgt resistance. However, constitutive activation of RLK-V1.1 resulted in the abnormal growth of transgenic plants.
Keywords: RLK-V; disease resistance; malectin-like/leucine-rich repeat receptor protein kinase; powdery mildew; wheat..
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