Soil-mediated Rhizobacteria Modulate SA-JA Transcriptional Antagonism in Tomato to Enhance Systemic Resistance Against a Specialist and a Generalist Herbivore

Abstract

Salicylic (SA) and jasmonic acid (JA) defense pathways antagonize each other to compromise host plant defense. Modulation of SA-JA transcriptional antagonism could enhance plant resistance against herbivores. Tomato, Solanum lycopersicum , was treated with phytohormonal inducers BTH (Benzothiadiazole-SA synthetic analogue) and MeJA (Methyl jasmonate-JA analogue) through foliar applications at 0, 0.5, and 1 mM, while PGP rhizobacteria ( Bacillus sp. Mb01 and Pseudomonas sp. Mb05) were applied through roots using a randomized block design having three replications. RNA transcripts of SA responsive genes ( PR1a and PAL ) and JA eliciting genes ( PIN2 and LOX ) were studied. Individual application of SA/JA synthetic analogues improved the levels of their respective marker genes but generated an antagonism by masking each other’s expression. Conversely, individual and combined treatment with rhizobacteria modulates SA/JA antagonism to enhance the expression of SA marker genes under MeJA treatment and of JA marker genes under BTH treatment. This improvement was tested against a specialist (whitefly, Bemisia tabaci ) and a generalist herbivore (tomato fruit borer, Helicoverpa armigera ) to assess enhanced pest resistance. Although SA and MeJA reduced the mean larval weight, larval survival, and adult emergence of H. armigera along with the mean nymph population of B. tabaci , the results were more pronounced when inducers were applied along with rhizobacteria. Instead of separate applications of BTH/MeJA, their combined application with PGPR is recommended to improve hostplant resistance against phytophagous pests. However, investigations on other SA and JA eliciting genes, PGPR species, and pests are required to implement these findings in a broader crop -pest spectrum.

Bibliographic Information