Transcriptomic and Metabolomic Responses in Cotton Plant to Apolygus lucorum Infestation

Abstract

With the wide-scale adoption of transgenic Bacillus thuringiensis (Bt) cotton, Apolygus lucorum (Meyer-Dür) has become the most serious pest and has caused extensive yield loss in cotton production. However, little is known about the defense responses of cotton at the seedling stage to A. lucorum feeding. In this study, to elucidate the cotton defense mechanism, cotton leaves were damaged by A. lucorum for 0, 4, 12 and 24 h. The transcriptomic results showed that A. lucorum feeding elicits a rapid and strong defense response in gene expression during the whole infestation process in cotton plants. Further analysis revealed that at each assessment time, more differentially expressed genes were up-regulated than down-regulated. The integrated analysis of transcriptomic and metabolic data showed that most of the genes involved in jasmonic acid (JA) biosynthesis were initially up-regulated, and this trend continued during an infestation. Meanwhile, the content levels of JA and its intermediate products were also significantly increased throughout the whole infestation process. The similar trend was displayed in condensed tannins biosynthesis. This research proved that, after plants are damaged by A. lucorum, the JA pathway mediates the defense mechanisms in cotton plants by promoting the accumulation of condensed tannins as a defense mechanism against A. lucorum. These results will help us to discover unknown defensive genes and improve the integrated pest management of A. lucorum.

Keywords: Apolygus lucorum; condensed tannins; cotton; induced resistance; jasmonic acid.

Figure 1

Transcriptomic and metabolomic overview of a time course of A. lucorum damage on cotton plants. (a) Total number of individual transcripts that were significantly up- or down-regulated at each time point. (b) Venn diagram illustrating the number of genes up-regulated during the time course. (c) Venn diagram illustrating the number of genes down-regulated during the time course. (d) Total number of metabolites that were significantly up- or down-regulated at each time point. (e) Venn diagram illustrating the number of metabolites up-regulated during the time course. (f) Venn diagram illustrating the number of metabolites down-regulated during the time course.

Figure 2

Clustering and classification of differentially expressed genes. The Roman numerals on the left indicate the class. The number in the top left corner in each panel indicates the identification number (ID), and the number in the bottom left corner of each panel indicates the number of genes in the cluster.

Figure 3

Plant phytohormones changed after A. lucorum feeding on cotton leaves. JA, jasmonic acid; JA-Ile, jasmonoyl-L-isoleucine; ABA, abscisic acid; SA, salicylic acid. Mean ± SE of n = 6; amounts with different letters were significantly different at the 5% level according to Tukey’s HSD test.

Figure 4

A. lucorum-induced responses in the jasmonic acid (JA) pathway. (a) Overview of the JA pathway. Metabolites shaded in green were measured. Solid arrows represent established biosynthesis steps, while broken arrows indicate the involvement of multiple enzymatic reactions. (b) Heat map of the expression of genes associated with the JA pathway. (c) Intermediate products contents in JA pathway cotton leaves. Values are mean ± SE of six biological replicates. Amounts with different letters were significantly different at the 5% level according to Tukey’s HSD test. Lipoxygenase (LOX); (9Z,11E,15Z)-(13S)-13-hydroperoxyoctadeca-9,11,15-rienoic acid (13(S)-HPOT); allene oxide synthase (AOS); (9Z,15Z)-(13S)-12,13-epoxyoctadeca-9,11,15-trienoic acid (12,13(S)-EOT); allene oxide cyclase (AOC); 12-oxo-10,15(Z)-phytodienoic acid (12-OPDA); 12-oxophytodienoate reductase (OPR); 8-[(1R,2R)-3-Oxo-2-{(Z)-pent-2-enyl}cyclopentyl]octanoate (OPC-8:0); OPC8-CoA ligase (OPCL); acyl-CoA oxidase (ACX); enoyl-CoA hydratase (MFP); acetyl-CoA acyl-transferase (fad A).

Figure 5

A. lucorum-induced responses in condensed tannins pathway. (a) Overview of the condensed tannins pathway. Metabolites shaded in green were measured. Solid arrows represent established biosynthesis steps, while broken arrows indicate the involvement of multiple enzymatic reactions. (b) Heat map of the expression of genes associated with the condensed tannins pathway. (c) Intermediate products contents in condensed tannins pathway cotton leaves. Values are mean ± SE of six biological replicates. Amounts with different letters were significantly different at the 5% level according to Tukey’s HSD test. L-phenylalanine ammonialyase (PAL), cinnamate 4−hydroxylase (C4H), 4−coumarate: CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone-3-hydroxylase (F3H), flavonoid 3′−hydroxylase (F3′H), dihydroflavonol reductase (DFR), anthocyanidin synthase (ANS), anthocyanidin reductase (ANR).