Molecular Responses to Aphid Feeding in Arabidopsis in Relation to Plant Defense Pathways

Abstract

Little is known about molecular responses in plants to phloem feeding by insects. The induction of genes associated with wound and pathogen response pathways was investigated following green peach aphid (Myzus persicae) feeding on Arabidopsis. Aphid feeding on rosette leaves induced transcription of two genes associated with salicylic acid (SA)dependent responses to pathogens (PR-1 and BGL2) 10-and 23-fold, respectively. Induction of PR-1 and BGL2 mRNA was reduced in npr1 mutant plants, which are deficient in SA signaling. Application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA, suggesting that wild-type SA-dependent responses do not influence resistance to aphids. Twofold increases occurred in mRNA levels of PDF1.2, which encodes defensin, a peptide involved in the jasmonate (JA)-/ethylene-dependent response pathway. Transcripts encoding JA-inducible lipoxygenase (LOX2) and SA/JA-inducible Phe-ammonia lyase increased 1.5to 2-fold. PDF1.2 and LOX2 induction by aphids did not occur in infested leaves of the JA-resistant coi1-1 mutant. Aphid feeding induced 10-fold increases in mRNA levels of a stress-related monosaccharide symporter gene, STP4. Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding.

Transcriptional Regulation of Sorghum Defense Determinants against a Phloem-Feeding Aphid

“…Higher chitinase and glucanase activities did not occur in greenbug-resistant sorghum (Krishnaveni et al, 1999). Likewise, induction of SA-dependent responses did not confer resistance to green peach aphid in Arabidopsis (Moran and Thompson, 2001). In contrast, control of insect pests including phloemfeeders by JA-regulated genes such as protease inhibitors has been established (Rahbe and Febvay, 1993;Tran et al, 1997).…”

“…A common feature among reported studies on plant-aphid interactions is that plants activate genes known to mount defenses against bacterial and fungal pathogens (Fidantsef et al, 1999;Moran and Thompson, 2001;Moran et al, 2002). Such a response is generally not stimulated by chewing insects (Reymond et al, 2000).…”

“…Thus, it is not unexpected that plants activate disparate responses when attacked by chewing versus phloem-feeding insects. However, using the Arabidopsis JA-insensitive mutant coi1-1, Moran and Thompson (2001) demonstrated involvement of the wounding pathway as well as SA-regulated genes in response to aphids. Furthermore, the whitefly (Bemisia argentifolii)-induced SLW3 gene from squash did not respond to any known defense-signaling molecules, implying that novel defense regulation could be elicited by phloem-feeding insects (van de Ven et al, 2000;Walling, 2000).…”

Categories of Resistance to Greenbug (Homoptera: Aphididae) Biotype I in <B> <I>Aegilops tauschii</I> </B> Germplasm

“…Indeed, expression of genes involved in sugar transport and metabolism were altered in GPA infested Arabidopsis (Moran and Thompson, 2001;Moran et al, 2002;Pegadaraju, 2005). The concentration of sucrose and starch increased in GPA-infested leaves of Arabi-dopsis (Singh et al, 2011).…”

Aphid Resistance inMedicago truncatulaInvolves Antixenosis and Phloem-Specific, Inducible Antibiosis, and Maps to a Single Locus Flanked by NBS-LRR Resistance Gene Analogs

“…This imbalance is starting to change, however, as molecular tools are applied to the study of induced responses to phloem feeding and to mechanisms of genetic resistance (for review, see Walling, 2000;Kessler and Baldwin, 2002;Moran et al, 2002). Studies with Arabidopsis (Arabidopsis thaliana) and cultivated species have identified changes in gene expression when plants are challenged with phloem feeders (Walling, 2000;Moran and Thompson, 2001;Moran et al, 2002;de Ilarduya et al, 2003;Zhu-Salzman et al, 2004). Considering the intimate and enduring contact of insect stylets with the host tissue, it is not surprising that these and other studies have found remarkable similarities between plant responses to phloem feeders and pathogens.…”