Advances in transcriptomics- and metabolomics-based exploration of plant responses to drought and herbivorous insects

Stress is an important environmental factor that restricts plant growth and development. Plant responses and adaptations to different stresses are complex and diverse. Under biotic and abiotic stresses, plants maintain homeostasis mainly by reallocating and adjusting a series of transcriptional regulatory networks and metabolic networks, resulting in changes at both the transcriptional and metabolic levels. With the development of omics techniques, transcriptomics, and metabolomics are widely used as emerging disciplines for studying plant adaptations to various stresses, which can aid in elucidating the molecular mechanisms of plant responses to stress at the transcriptional and metabolic levels. Among the various stresses that plants face, drought, and insect pests are particularly severe, causing significant losses in agricultural production. In this review, we summarize the transcriptional and metabolic regulatory mechanisms of plants under single drought stress, insect herbivory stress, or dual drought and insect herbivory stresses. Plants respond to drought stress by regulating the expression of genes related to the synthesis of abscisic acid, proline, photosynthetic intermediates, and their metabolites. Moreover, plants respond to phytophagous insect attacks by regulating the expression of genes participating in the synthesis of jasmonic acid, salicylic acid, flavonoids, and their metabolites. Under dual stresses, plants regulate hormone interactions and the production of secondary metabolites to reinforce resistance against herbivory under drought stress. Exploring transcriptional and metabolic differences and their key regulatory factors in plant adaptations to adverse stress can provide a theoretical basis and reference for breeding varieties tolerant to adverse stress and with improved crop yields.