No abstract

The basal defenses important in curtailing the development of the phloem-feeding silverleaf whitefly (Bemisia tabaci type B; SLWF) on Arabidopsis (Arabidopsis thaliana) were investigated. Sentinel defense gene RNAs were monitored in SLWF-infested and control plants. Salicylic acid (SA)-responsive gene transcripts accumulated locally (PR1, BGL2, PR5, SID2, EDS5, PAD4) and systemically (PR1, BGL2, PR5) during SLWF nymph feeding. In contrast, jasmonic acid (JA)- and ethylene-dependent RNAs (PDF1.2, VSP1, HEL, THI2.1, FAD3, ERS1, ERF1) were repressed or not modulated in SLWF-infested leaves. To test for a role of SA and JA pathways in basal defense, SLWF development on mutant and transgenic lines that constitutively activate or impair defense pathways was determined. By monitoring the percentage of SLWF nymphs in each instar, we show that mutants that activate SA defenses (cim10) or impair JA defenses (coi1) accelerated SLWF nymphal development. Reciprocally, mutants that activate JA defenses (cev1) or impair SA defenses (npr1, NahG) slowed SLWF nymphal development. Furthermore, when npr1 plants, which do not activate downstream SA defenses, were treated with methyl jasmonate, a dramatic delay in nymph development was observed. Collectively, these results showed that SLWF-repressed, JA-regulated defenses were associated with basal defense to the SLWF.

Phytophages breach the integrity of plant tissues to recover nutrients from foliage, seeds, pollen, nectar, roots, or shoots. While many herbivores cause extensive damage, phloem-feeding insects, such as aphids and whiteflies, cause modest to barely perceptible damage, respectively. Phloem-feeding insects provide additional challenges to plants as they deplete photosynthates, vector viruses, and introduce chemical and/ or protein effectors that alter plant defense signaling, infestation symptoms, and plant development (Kaloshian and Walling, 2005). When these attributes are combined with broad host ranges, breeding strategies that promote invasiveness, highly evolved feeding strategies, the ability to adapt to a wide range of plant habitats, and the emergence of insecticide-resistant strains, it is not surprising that phloem-feeding insects cause heavy losses in agriculture and horticulture (Goggin, 2007).With the tools of cell and molecular biology, genetics, genomics, electrophysiology, and biochemistry, investigators are providing novel insights into the complexity and dynamics of plant-herbivore interactions. Many of the reviews in this issue describe the initial events in perception, as well as the defense signals and biochemical reprogramming that influence direct (antibiotic and antixenotic) and indirect (interactions with natural enemies) defenses to tissue-damaging herbivores. This review will highlight intricacies of plant-/phloemfeeding insect interactions, with a primary focus on whiteflies and comparisons to aphids.Although whiteflies and aphids are members of the Hemipteran suborder Sternorrhyncha, their life cycles, endosymbiont populations, and feeding activities are distinct (Baumann, 2005;Kaloshian and Walling, 2005). These insects use highly modified mouthparts (stylets) to navigate the cuticle, epidermis, and mesophyll and establish feeding sites in phloem sieve elements (SEs).Aphid adults and nymphs are mobile and utilize several feeding sites during their lifetime. In contrast, once the whitefly nymph establishes a feeding site on a minor vein of the phloem, nymphs (first-fourth instars) feed at this site almost continuously for 21 to 30 d (Fig. 1). The immobility of nymphs, longer life cycle, and prolonged nymph feeding are features that distinguish the whitefly-plant and aphid-plant interactions.Aphids and whiteflies take advantage of their adept feeding strategies and avoid or deter many plant defenses. These insects disguise themselves and deceive their hosts and natural enemies by using their stylets to deliver salivary chemicals and/or proteins into the plant to influence wound healing, defense-signaling pathways, and volatile emissions. Similar deceptive strategies are routinely employed by phytopathogenic microbes to avoid recognition and combat plant defenses (da Cunha et al., 2007). Pathogens introduce effectors into plant cells manipulating many biochemical and cellular processes to enhance phytopathogen success on host plants. In plant-biotroph interactions, effectors influence ...