Abstract
Chickpea (C. arietinum L.) is an important pulse crop in Asian and African countries that suffers significant yield losses due to attacks by insects like H. armigera. To obtain insights into early responses of chickpea to insect attack, a transcriptomic analysis of chickpea leaves just 20 minutes after simulated herbivory was performed, using oral secretions of H. armigera coupled with mechanical wounding. Expression profiles revealed differential regulation of 8.4% of the total leaf transcriptome with 1334 genes up-regulated and 501 down-regulated upon wounding at log2-fold change (|FC| ≤ −1 and ≥1) and FDR value ≤ 0.05. In silico analysis showed the activation of defenses through up-regulation of genes of the phenylpropanoid pathway, pathogenesis, oxidases and CYTP450 besides differential regulation of kinases, phosphatases and transcription factors of the WRKY, MYB, ERFs, bZIP families. A substantial change in the regulation of hormonal networks was observed with up-regulation of JA and ethylene pathways and suppression of growth associated hormone pathways like GA and auxin within 20 minutes of wounding. Secondary qPCR comparison of selected genes showed that oral secretions often increased differential expression relative to mechanical damage alone. The studies provide new insights into early wound responses in chickpea.
Highlights
Earlier studies showed a considerable overlap in differentially expressed genes after various stresses such as wounding, herbivory or pathogen attack[8,21]
We show the activation of pathways related to defense and hormones like jasmonic acid (JA) and ethylene and simultaneous suppression of growth related hormones of gibberelic acid (GA) and auxin within minutes of wounding
The analysis indicated a prominent up-regulation of the JA and ethylene pathways both at the level of biosynthesis and response/signaling with an over-representation in the wound-responsive transcriptome (Fig. 5)
Summary
Earlier studies showed a considerable overlap in differentially expressed genes after various stresses such as wounding, herbivory or pathogen attack[8,21]. Two different plants of the Solanaceous group responded to an attack of the same Lepidopteran herbivore by a species-specific differential gene expression pattern[27]. The changes occurring within minutes of insect wounding, important, have been far less characterized. These are important to understand how early wound signals are transmitted and to isolate early wound responsive promoters that could be more effective in targeting insect larvae within minutes of attack than conventionally used constitutive promoters for expression for insecticidal genes. The study represents an important resource for understanding wound responses in legumes for use in improvement of several crops
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