Arabidopsis Transcription Factor MYB102 Increases Plant Susceptibility to Aphids by Substantial Activation of Ethylene Biosynthesis

Abstract

Induction of ethylene biosynthesis by aphids increases the susceptibility of several plant species to aphids. Recent studies have indicated that some MYB transcription factors regulate the phloem-based defense against aphid infestation by modulating ethylene (ET) signaling. Arabidopsis MYB102 has previously been shown to be induced by wound signaling and regulate defense response against chewing insects. However, it remains unclear whether ArabidopsisMYB102 takes part in the defense response of plants to aphids. Here, we investigated the function of MYB102 in the response of Arabidopsis to aphid infestation. ArabidopsisMYB102 was primarily expressed in vascular tissues, and its transcription was remarkably induced by green peach aphids (GPA; Myzus persicae). The results of RNA-Sequencing revealed that overexpression of MYB102 in Arabidopsis promoted ET biosynthesis by upregulation of some 1-aminocyclopropane-1-carboxylate synthase (ACS) genes, which are rate-limiting enzymes of the ET-synthetic pathway. Enhanced ET levels led to reduced Arabidopsis resistance to GPA. Furthermore, dominant suppression of MYB102 inhibited aphid-induced increase of ET levels in Arabidopsis. In agreement with a negative regulatory role for ET in aphid defense responses, the MYB102-overexpressing lines were more susceptible to GPA than wild-type (WT) plants. Overexpression of MYB102 in Arabidopsis obviously repressed aphid-induced callose deposition. Conversely, overexpression of MYB102 failed to increase aphid susceptibility in both the ET-insensitive mutants and plants treated with inhibitors of ET signaling pathways, demonstrating that the ET was critical for promoting aphid performance conferred by overexpression of MYB102. Collectively, our findings indicate that the Arabidopsis MYB102 increases host susceptibility to GPA through the ET-dependent signaling pathways.

Keywords: 1-aminocyclopropane-1-carboxylate synthase; Myzus persicae; aphid susceptibility; ethylene; host resistance.

Figure 1

Detection of MYB102 promoter activity by glucuronidase (GUS) staining. GUS activity driven by MYB102 promoter in five-day-old seedlings (a), 14-day-old seedlings (b), vascular tissues in leaves of five- (c) and 14-day-old seedlings (d), stomata in leaves of 5-day-old seedlings (e), leaves of 14-day-old seedlings (f), flowers (g), siliques (h), petals (i), primary roots (j), lateral roots (k), and vascular tissues in roots (l).

Figure 2

The transcription of MYB102 in response to aphid infestation. Quantitative Real Time- Polymerase Chain Reaction (qRT-PCR) analysis of MYB102 expression relative to that of ACTIN2 in uninfested and aphid-infested leaves of Arabidopsis plants carrying pMYB102:GUS at the indicated time post-infestation. Values are mean ± SD (standard deviation), n = 3. Different letters above bars denote significant difference among different treatments using Tukey’s test at p < 0.05.

Figure 3

Overexpression of MYB102 increases Arabidopsis susceptibility to aphid infestation. (a) Aphid population size (adults plus nymphs) reared on the WT, myb102, and MYB102-OX lines (n = 10) after 48 h of infestation. (b) The number of progeny from initially one female per plant was measured after 10 days of nymph infestation (n = 10). (c) Average body weight of adult aphids on the WT, myb102, and two independent MYB102-OX and -SRDX lines (n = 10) after 48 h of infestation (d) Aphid population size on the WT, myb102, and two independent MYB102-SRDX lines (n = 10) after 48 h of infestation. Different letters above bars denotes significant difference among different treatments using Tukey test at p < 0.05.

Figure 4

Analyses of differentially expressed genes (DEGs) between the wild-type (WT) and MYB102-OX3 lines. (a) Volcano plot showing up- and down-regulated DEGs. The x-axis indicated the value of log2 (OX3/WT), and the y-axis indicated the value of −log10 (1-probability). (b) Statistics of up- and down-regulated DEGs. The x-axis indicated downregulated and upregulated genes, and the y-axis indicated the number of DEGs. (c) Most enriched Gene Ontology (GO) terms of DEGs were categorized into biological process, cellular component, and molecular function. The x-axis indicates GO terms and the y-axis indicates the percent of genes in all the DEGs.

Figure 5

Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of differentially expressed genes between the WT and MYB102-OX3 lines. Size and color of the bubble indicated the amount of DEGs enriched in pathway and enrichment significance, respectively.

Figure 6

Overexpression of MYB102 increases ethylene (ET) production in uninfested and aphid-infested Arabidopsis plants. The content of salicylic acid (SA) (a), jasmonic acid (JA) (b), ET (c), and abscisic acid (ABA) (d) was determined in the WT, myb102, MYB102-OX and -SRDX lines after zero and 48 h of aphid infestation. At least three replicates were conducted for each genotype. Different letters above bars denotes significant difference among different treatments using Tukey’s test at p < 0.05.

Figure 7

Overexpression of MYB102 upregulates the expression of ET biosynthetic genes in Arabidopsis. Relative expression levels of ACS4 (a), ACS7 (b), ACS8 (c), and ACS11 (d) were examined in the WT, myb102, MYB102-OX and -SRDX lines after 0 and 48 h of aphid infestation. Different letters above bars denotes significant difference among different treatments using Tukey’s test at p < 0.05.

Figure 8

ET signaling is essential for increasing Arabidopsis susceptibility to aphids conferred by overexpression of MYB102. (a) Population size (adults plus nymphs) of adult aphids on WT, MYB102-OX lines, MYB102-OX/ein2–1, and MYB102-OX/etr1–3 (n = 10) after 48 h of infestation, and (b) the number of progeny nymphs reared on these plants was measured after 10 days of nymph infestation (n = 10). (c) Population size (adults plus nymphs) of adult aphids on both the WT and MYB102-OX lines, MCP- or AVG-treated MYB102-OX lines after 48 h of infestation, and (d) the number of progeny nymphs was calculated after 10 days of nymph infestation (n = 10). Different letters above bars denotes significant difference among different treatments using Tukey’s test at p < 0.05.

Figure 9

ET signaling is required for inhibiting callose accumulation by overexpression of MYB102. (a) Callose deposition in leaves of WT, MYB102-OX lines, MYB102-OX/ein2–1, and MYB102-OX/etr1–3 (n = 10) after 48 h of aphid infestation. (b) Callose deposition in leaves of WT and MYB102-OX lines with or without treatments with 1-methylcyclopropene (MCP) or aminoethoxyvinyl glycine (AVG). Different letters above bars denotes significant difference among different treatments using Tukey’s test at p < 0.05.