Elucidation of quorum sensing components and their role in regulation of symbiotically important traits in Ensifer nodulating pigeon pea.

Quorum sensing (QS) in rhizobia regulates diverse processes determining the success and efficiency of association with the legume host. Despite the notable importance of QS as well as the well-known underlying variability in the genomic and metabolic components thereof, its study in rhizobia is largely restricted to few laboratory strains. In this work, QS phenomenon in the rhizobia nodulating pigeon pea- one of the most important legume crops of the global-south, is characterized. Using 16S rRNA and recombinaseA sequencing analysis, the selected QS-positive and host-beneficial isolates were identified to be taxonomically affiliated to the genus Ensifer. Their QS components, including homologues of QS genes, and the repertoire of N-acyl homoserine lactone (AHL) autoinducers were identified. Sequences of the QS homologues showed significant variabilities ranging from 10 to >20% with the known Ensifer sequences. Autoinducer profiling using LC-MS/MS revealed the production of long and short chain AHLs variably by the isolates, including 3-oxo-C12-homoserine lactone (3-O-C12-HSL) and 3-OH-C16-HSL as their first report in Rhizobiaceae. Motility and attachment- two of the most crucial traits for effective establishment on host roots were discovered to be QS dependent in in vitro analysis and the same was confirmed using expression analysis of their regulatory genes using qRT-PCR; both revealing a QS mediated repression of motility and promotion of attachment. This study highlights that Ensifer nodulating pigeon pea, although with significant variance in the anatomy of their QS components, regulate symbiotically crucial cell-processes via QS in a scheme that is conserved in multiple genera.