LysM Domain Receptor Kinases Regulating Rhizobial Nod Factor-Induced Infection

TLDR

The rhizobial infection of legumes is highly dependent on Nod factor structure, prompting the proposal of a specific Nod factor entry receptor, with SYM2 in pea identified as a candidate. The study aimed to identify genes specifically involved in rhizobial infection by leveraging the phylogenetic similarity between pea and Medicago truncatula. The authors examined the SYM2 orthologous region in Medicago truncatula, identifying 15 receptor‑like genes, including 7 LysM domain–containing receptor‑like kinases. Reverse genetics in Medicago truncatula revealed that two LYK genes are essential for infection thread formation, indicating they function as Nod factor entry receptors.

Abstract

The rhizobial infection of legumes has the most stringent demand toward Nod factor structure of all host responses, and therefore a specific Nod factor entry receptor has been proposed. The SYM2 gene identified in certain ecotypes of pea ( Pisum sativum ) is a good candidate for such an entry receptor. We exploited the close phylogenetic relationship of pea and the model legume Medicago truncatula to identify genes specifically involved in rhizobial infection. The SYM2 orthologous region of M. truncatula contains 15 putative receptor-like genes, of which 7 are LysM domain–containing receptor-like kinases (LYKs). Using reverse genetics in M. truncatula , we show that two LYK genes are specifically involved in infection thread formation. This, as well as the properties of the LysM domains, strongly suggests that they are Nod factor entry receptors.