Enzymatic characterization of the saliva of the eriophyid mite, Aceria pongamiae Keifer1966 (Acari: Eriophyidae) and the bacterial endobiome of the galls induced on Pongamia pinnata (L.) Pierre (Fabaceae)

Galls, like other regular plant organs, possess their own histological and physiological features. A high degree of specificity is maintained between the host and the inducer, and hence gall morphogenesis is highly conserved and would help trace gall lineages and cell fate. The present study highlights the induction and subsequent development of leaf galls on the Indian Beech tree, Pongamia pinnata (L) Pierre (Fabaceae), mediated through the active participation of a gall-inducing species of eriophyid mite, Aceria pongamiae Keifer and gall-associated bacterial endobiome. The saliva of A. pongamiae and selected strains of gall-associated bacterial endobiome were characterized in part during the study. Three strains of Staphylococcus arlettae (PGP1-3) and one strain of Bacillus flexus (PGP4) were identified from the leaf galls through 16S rDNA sequencing. The mite saliva displayed tryptophanase activity, and the bacterial strains showed differential enzyme activities (protease, amylase, cellulase, DNAse, pectinase, tryptophanase, and catalase). All four strains of bacterial endobiome exhibited unique metal tolerance as well as pH and temperature regulating activity. Evaluation of the potential role of the mite saliva and the gall associated bacterial endobiome in gallogenesis was done by monitoring the plant growth-promoting activity of the salivary extract and the isolated bacterial strains through in vitro seed (Vigna radiata) germination assay. Salivary extract of the mite showed the highest rate of plant growth-promoting activity compared with that of the isolated strains of bacterial endobiome. The present study forms the first attempt that illustrates the characteristic features of the saliva of the gall inducer and the gall associated bacterial endobiome. Based on the results of the current study, we suggest that eriophyid mite saliva and the gall-associated microbes play significant roles in the induction of cecidia.