Abstract
Many secondary metabolites have insecticidal efficacy against pests and may be affected by abiotic stress. However, little is known of how plants may respond to such stress as pertains the growth and development of pests. The objective of this study was to determine if and how salt stress on cotton plants affects the population dynamics of aphids. The NaCl treatment (50mM, 100mM, 150mM and 200mM) increased contents of gossypol in cotton by 26.8–51.4%, flavonoids by 22.5–37.6% and tannic by 15.1–24.3% at 7–28 d after salt stress. Compared with non-stressed plants, the population of aphids on 150 and 200 mM NaCl stressed plants was reduced by 46.4 and 65.4% at 7d and by 97.3 and 100% at 14 days after infestation. Reductions in aphid population were possibly attributed to the elevated secondary metabolism under salt stress. A total of 796 clones for aphids transcriptome, 412 clones in the positive- library (TEST) and 384 clones in the reverse-library (Ck), were obtained from subtracted cDNA libraries and sequenced. Gene ontology (GO) functional classification and KEGG pathway analysis showed more genes related to fatty acid and lipid biosynthesis, and fewer genes related to carbohydrate metabolism, amino acid metabolism, energy metabolism and cell motility pathways in TEST than in Ck library, which might be the reason of aphids population reduction. A comparative analysis with qRT-PCR indicated high expression of transcripts CYP6A14, CYP6A13, CYP303A1, NADH dehydrogenase and fatty acid synthase in the TEST group. However, CYP307A1 and two ecdysone-induced protein genes were down regulated. The results indicate that genes of aphids related to growth and development can express at a higher level in reaction to the enhanced secondary metabolism in cotton under salinity stress. The expression of CYP307A1 was positively correlated with the population dynamics of aphids since it was involved in ecdysone synthesis.
Highlights
Secondary metabolism is a distinctive process in the growth and development of plant species including cotton, and in their adaptation to the environment [1]
Our findings indicate that the reduced severity of aphid infestation in cotton plants might be attributed to the enhanced level of secondary metabolites as indicated with increased levels of gossypol, flavonoids and tannin in cotton tissues under salt stress
Genes responsible for the growth and development of aphids expressed at a higher level against the enhanced secondary metabolism under salinity stress
Summary
Secondary metabolism is a distinctive process in the growth and development of plant species including cotton, and in their adaptation to the environment [1]. Apart from self-regulations by cotton plant, secondary metabolisms are influenced by biotic and abiotic environmental factors [2,3], and provide considerable defense against pests [4,5,6]. Increasing CO2 levels increased the condensed tannin and gossypol content in cotton plants, and reduced the growth and development of infesting Aphids gossypii indirectly [12]. A reduction in the levels of induced terpenoids due to lack of target herbivore induction in Bt cotton increased aphid population [13]. Compared with non-transgenic cotton, the reductions in gossypol and tannin contents of Bt cotton favored the development of Tetranychus cinnaberinus mites [18]
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