Transcriptomics and functional genomics of plant defence induction by phloem-feeding insects.

The relationship between phloem-feeding insects (PFIs) and plants offers an intriguing example of a highly specialized biotic interaction. These insects have evolved to survive on a nutritionally imbalanced diet of phloem sap, and to minimize wound responses in their host plants. As a consequence, plant perception of and responses to PFIs differ from plant interactions with other insect-feeding guilds. Transcriptome-wide analyses of gene expression are currently being applied to characterize plant responses to PFIs in crop plants with race-specific innate resistance, as well as in compatible interactions with susceptible hosts. Recent studies indicate that PFIs induce transcriptional reprogramming in their host plants, and that plant responses to PFIs appear to be quantitatively and qualitatively different from responses to other insects or pathogens. Transcript profiling studies also suggest that PFIs induce cell wall modifications, reduce photosynthetic activity, manipulate source-sink relations, and modify secondary metabolism in their hosts, and many of these responses appear to occur within the phloem tissue. Plant responses to these insects appear to be regulated in part by the salicylate, jasmonate, and ethylene signalling pathways. As additional transcript profiling data become available, forward and reverse genetic approaches will be necessary to determine which changes in gene expression influence resistance or susceptibility to PFIs.