Transcription Factor MYB44and Glucan Synthase-Like Enzyme GSL5Regulate Defense Response To Myzus Persicae In Arabidopsis

We have investigated37ethylene-inducible Arabidopsis transcription factor genes for effect on the activation of ethylene signaling and insect defense, and the AtMYB44gene is most induced. Special GLUCAN SYNTHESIS-LIKE (GSL) genes and p-1,3-glucan callose play an important role in plant defense responses to attacks by phloem-feeding insects. HrpNEa is a harpin produced by Erwinia amylovora, which can stimulate different signaling pathways to confer various beneficial effects. Treatment of plants with HrpNEa induces Arabidopsis resistance to the green peach aphid by activating the ethylene signaling pathway.In response to the phloem-feeding stress, plants defend themselves by using the phloem-based defense mechanism. This mechanism involves the biosynthesis of β-1,3-glucan callose and subsequent closure of sieve pores and coagulation on sieve plates. Biochemical evidence and molecular studies in several plants pecies indicate that callose is synthesized by a class of enzymes, termed callose synthases or glucan synthases. Twelve genes encoding putative glucan synthase have been identified and designated as AtGSLl through AtGSL12in Arabidopsis.One of the main purposes of this study was to elucidate if AtGSL and callose play a role in HrpNEa-induced resistance to M. persicae in Arabidopsis. We present evidence that AtGSL5is required for HrpNEa-induced repression in aphid feeding activities.In Arabidopsis thaliana (Arabidopsis) treated with the harpin protein HrpNEa, resistance to the green peach aphid Myzus persicae, a generalist phloem-feeding insect, develops with induced expression of the AtMYB44gene. However, atmyb44was an mutant with an abrogation in HrpNEa-induced EIN2expression, suggesting a close relationship between AtMYB44and EIN2.This study provides further materials and evidences for research of relationship between AtMYB44and ethylene pathways in the plant development and signal transduction.In24-hour successive surveys on large-scale aphid populations, the proportion of feeding aphids was much smaller in HrpNEa-treated plants than in control plants, and aphids preferred to feed from37atgsl mutants tested rather than the wild-type plant, in the24-hour survey, both atgsl5and atgsl6performed to tolerate aphid feeding while atgsl5was the most tolerant. Consistently, atgsl5was also most inhibitive to the deterrent effect of HrpNEa on the phloem-feeding activity of aphids monitored by the electrical penetration graph technique. Theses results suggested an important role of the AtGSL5gene in the effect of HrpNEa. In response to HrpNEa, AtGSL5expression and callose deposition were induced in the wild-type plant but not in atgsl5. In response to HrpNEa, moreover, the AtMYB44gene known as required for repression of aphid reproduction on the plant was also required for repression of the phloem-feeding activity. Little amounts of the AtGSL5transcript and callose deposition were detected in the atmyb44mutant as in atgsl5. Both mutants performed similarly in tolerating the phloem-feeding activity and impairing the deterrent effect of HrpNEa, suggesting that AtGSL5and AtMYB44both contributed to the effect.We will prepare to further investigate these plants, establishing the genetic connection between AtMYB44regulation for EIN2and development of the plant resistance. We use the methods of artificial pollination to pollinate the ethylene-insensitive mutants of ein2-1, ein3-1, ein5-1. The pollen is from MYB44OTA. We successfully obtain hybrid strains of MYB44OTA ein2-1, MYB44OTA ein3-1and MYB44OTA ein5-1.