Sodium chloride primes JA-independent defense against Spodoptera litura (Fabricius) larvae in Arabidopsis thaliana

Abstract

Priming for better defense performance is an important strategy in acclimation to the ever-changing environment. In the present study, defense priming induced by sodium chloride at the seedling stage significantly increased the expression of defense gene VSP2, the content of total glucosinolates and the level of the reactive oxygen species in mature Arabidopsis thaliana plants after transferred into the stress-free environment. The previously primed plants could effectively resist the feeding of Spodoptera litura (Fabricius) larvae. Salt-priming enhanced defense of Arabidopsis plants in the absence of either MYC2 or AOS, which encodes a critical transcription factor in JA-signaling and an important enzyme in JA biosynthesis, respectively. Our results supported the JA-independent defense primed by sodium chloride, as well as the elevated ROS and glucosinolate level in primed plants. In addition, the feasibility of using mild salt-priming to improve crop performance in field was proposed.

Keywords: Sodium chloride; defense priming; herbivory; jasmonic acid pathway.

Figure 1.

Sodium chloride primes Arabidopsis plants against Spodoptera litura larval feeding. Arabidopsis eight-rosette-leave plants were fed by second instar larvae of Spodoptera litura (Fabricius). (a) Primed plants and non-primed plants on the fourth day after infestation. (b) Rosette leaf damage caused by larval feeding in primed plants and non-primed plants. (c) Larval growth assessment after feeding on primed plants and non-primed plants. The scale bar represents 5 mm. Ten larvae were used to calculate mean values and standard deviations. Feeding assay was replicated above 3 times. Error bars indicate the standard deviation. ** differences are highly significant (P < .01) by Dunnett’s multiple comparison test. dai: days after infection by larvae. NP: non-primed plants; P: primed plants.

Figure 2.

Primed defense responses of Arabidopsis aos and myc2 mutants. Arabidopsis eight-rosette-leave plants were fed by second instar larvae of Spodoptera litura (Fabricius). (a) Primed plants and non-primed plants on the fourth day after infestation. (b) Rosette leaf damage measurement by ImageJ. (c) Larvae on the fourth day after infestation; the scale bar represents 5 mm. (d) Larval growth assessment after feeding on primed plants and non-primed plants. Ten larvae were used to calculate mean values and standard deviations. Feeding assay was replicated above 3 times. (e) Relative expression levels of VSP2 in primed plants and non-primed plants in wild type Col-0 and two mutants, aos and myc2. Error bars indicate the standard deviation. ** differences are highly significant (P< .01) by Dunnett’s multiple comparison test. dai: days after infection by larvae. NP: non-primed plants; P: primed plants.

Figure 3.

ROS and GSL in non-primed and primed plants. (a) DAB staining of leaves from Arabidopsis seedlings and mature plants with (P) or without (NP) 100 mM NaCl for 10 days; DAB staining of non-primed or primed plants at eight-rosette-leave stage. The scale bar represents 1 mm. (b) H₂O₂ content in non-primed plants. (c) Relative expression levels of RBOHA, RBOHB, RBOHC, SOD2 and CAT1 in non-primed and primed Arbidopsis at eight-rosette-leave stage. (d) Total glucosinolate content in Arabidopsis at eight-rosette-leave satge. (e) The expression of key genes SUR1 and FMO (FMOGS-OX3) related to glucosinolate synthesis in leaves of non-primed and primed plants at eight-rosette-leave stage. All tests were replicated three times. Error bars indicate the standard deviation. **differences are significant (P < .01) by Dunnett’s multiple comparison test.