Biochemical dynamics during development of insect-induced plant galls: a review

Abstract

Insect-induced galls are regulated outgrowths of plant tissues that result from unique and mutual interactions between host plants and gall-inducing insects. The insects, mainly belonging to the orders Hemiptera, Hymenoptera, Thysanoptera, and Diptera, induce gall formation through activities such as oviposition, feeding, secretions, and chewing. These activities trigger morphogenetic and physiological factors, leading to the development of distinct forms of galls. It is noteworthy that about 90% of gall-inducing insects exhibit host specificity. This review investigates the biochemical and metabolic changes that occur when plants and insects interact. These insects use enzymes such as polygalacturonase, pectinesterase, cellulase, and proteinase present in their saliva to assist in breaking down the plant's cuticle and cell wall during the infestation. This process disrupts the subcellular environment, resulting in a chemical shock at the infestation sites. Stressful conditions stimulate the generation of action potential in plants, activating channels and causing faster depolarization of the plasma membrane. Additionally, under stress, plants may generate high levels of reactive oxygen species (ROS), leading to an oxidative burst at sites of infection. ROS triggers necrosis through a hypersensitive response. Gall-inducing insects disrupt the normal metabolism of host plants, resulting in a series of biochemical changes and metabolic imbalances. These changes promote the formation of new plant tissues, which require the production of plant growth hormones and ultimately alter the host plant's phenotype.