Abstract
Plant-associated beneficial microbes have been explored to fulfill the imperative function for plant health. However, their impact on the host secondary metabolite production and nematode disease management remains elusive. Our present work has shown that chitinolytic microbes viz., Chitiniphilus sp. MTN22 and Streptomyces sp. MTN14 singly as well as in combination modulated the biosynthetic pathway of bacoside A and systemic defense mechanism against Meloidogyne incognita in Bacopa monnieri. Interestingly, expression of bacoside biosynthetic pathway genes (3-Hydroxy-3-methylglutaryl coenzyme A reductase, mevalonate diphosphate decarboxylase, and squalene synthase) were upregulated in plants treated with the microbial combination in the presence as well as in absence of M. incognita stress. These microbes not only augmented bacoside A production (1.5 fold) but also strengthened host resistance via enhancement in chlorophyll a, defense enzymes and phenolic compounds like gallic acid, syringic acid, ferulic acid and cinnamic acid. Furthermore, elevated lignification and callose deposition in the microbial combination treated plants corroborate well with the above findings. Overall, the results provide novel insights into the underlying mechanisms of priming by beneficial microbes and underscore their capacity to trigger bacoside A production in B. monnieri under biotic stress.
Highlights
Exploitation of beneficial microbes is well known to promote productivity, ameliorate nutrient supply and defend host from the various stresses
The most efficient control of M. incognita was observed in the microbial combination treated plants which (P ≤ 0.05) reduced the root galling index (RGI) by 2.8 fold, followed by alone Chitiniphilus sp. and Streptomyces sp. treatments which demonstrated reduction by 1.7 and 1.5 fold, respectively against untreated M. incognita control (Supplementary Table S1)
Analysis of the data revealed that higher activity was found in the microbial combination treated plants with pathogen followed by alone treatments compared to untreated M. incognita stressed plants (Supplementary Table S2)
Summary
Exploitation of beneficial microbes is well known to promote productivity, ameliorate nutrient supply and defend host from the various stresses. The use of microbes for boosting in planta secondary metabolite production under biotic stress could be a better and sustainable approach. To keep pace with the growing demand of this medicinal plant and considering its ability to grow under natural conditions, the present study was undertaken to develop strategies to improve yields of B. monnieri through beneficial microbial intervention. Till date, no information is available regarding the potential and possible mechanisms of the synergistic mode of microbes in the accumulation of secondary metabolites along with the modulation of the defense signaling pathway to endure biotic stress. Considering the above facts, efforts were made to examine the effect of synergistic chitinolytic microbial combination on induction of in planta bacoside A production and the possible mechanism adopted by B. monnieri plants under M. incognita stress
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