Salicylic acids: local, systemic or inter-systemic regulators?

Abstract

Salicylic acid is well known phytohormone, emerging recently as a new paradigm of an array of manifestations of growth regulators. The area unleashed yet encompassed the applied agriculture sector to find the roles to strengthen the crops against plethora of abiotic and biotic stresses. The skipped part of integrated picture, however, was the evolutionary insight of salicylic acid to either allow or discard the microbial invasion depending upon various internal factors of two interactants under the prevailing external conditions. The metabolic status that allows the host invasion either as pathogenesis or symbiosis with possible intermediary stages in close systems has been tried to underpin here.

Figure 1. Multiple factors determine the fate of relationship between two interactants (macrobiont and microbiont) i.e., environmental conditions, genotype of two and the time duration.

Figure 2. Major biological kingdoms interacts though simple organization/microbes (at base) more commonly with three multi-organized kingdoms to co-evolve chronologically diverse interactions in the nature. The horizontal genetic interchange is seems to be stabilized by the vertical gene transfer and epigenetic expressions under diverse environmental regimes on earth.

Figure 3. Two most important microbial interactants of plants i.e., root noduling rhizobium and VAM fungi shares the signaling pathways converging at key factors.