Plants perceive and respond to volatile signals in their environment. Herbivore-infested plants release volatile organic compounds (VOCs) which can initiate systemic defense reactions within the plant and contribute to plant-plant communication. Here, for Ipomoea batatas (sweet potato) leaves we show that among various herbivory-induced plant volatiles, (E)-4,8–dimethyl–1,3,7-nonatriene (DMNT) had the highest abundance of all emitted compounds. This homoterpene was found being sufficient for a volatile-mediated systemic induction of defensive Sporamin protease inhibitor activity in neighboring sweet potato plants. The systemic induction is jasmonate independent and does not need any priming-related challenge. Induced emission and responsiveness to DMNT is restricted to a herbivory-resistant cultivar (Tainong 57), while a susceptible cultivar, Tainong 66, neither emitted amounts comparable to Tainong 57, nor showed reaction to DMNT. This is consistent with the finding that Spodoptera larvae feeding on DMNT-exposed cultivars gain significantly less weight on Tainong 57 compared to Tainong 66. Our results indicate a highly specific, single volatile-mediated plant-plant communication in sweet potato.

IbNAC1 is known to activate the defense system by reprogramming a genetic network against herbivory in sweet potato. This regulatory activity elevates plant defense potential but relatively weakens plants by IbNAC1-mediated JA response. The mechanism controlling IbNAC1 expression to balance plant vitality and survival remains unclear. In this study, a wound-responsive G-box cis-element in the IbNAC1 promoter from -1484 to -1479 bp was identified. From a screen of wound-activated transcriptomic data, one transcriptional activator, IbbHLH3, and one repressor, IbbHLH4, were selected that bind to and activate or repress, respectively, the G-box motif in the IbNAC1 promoter to modulate the IbNAC1-mediated response. In the early wound response, the IbbHLH3-IbbHLH3 protein complex binds to the G-box motif to activate IbNAC1 expression. Thus, an elegant defense network is activated against wounding stress. Until the late stages of wounding, IbbHLH4 interacts with IbbHLH3, and the IbbHLH3-IbbHLH4 heterodimer competes with the IbbHLH3-IbbHLH3 complex to bind the G-box and suppress IbNAC1 expression and timely terminates the defense network. Moreover, the JAZs and IbEIL1 proteins interact with IbbHLH3 to repress the transactivation function of IbbHLH3 in non-wounded condition, but their transcription is immediately inhibited upon early wounding. Our work provides a genetic model that accurately switches the regulatory mechanism of IbNAC1 expression to adjust wounding physiology and represents a delicate defense regulatory network in plants. Plants develop sophisticated defense systems against insect attack. IbNAC1 is a transcriptional activator, which up-regulates sporamin expression against herbivory in sweet potato. However, it simultaneously injures the plant by IbNAC1-induced JA response. Thus, dynamic regulatory networks to coordinate the expression of IbNAC1 are essential for appropriate growth and defense in sweet potato. Here, two bHLH transcription factors, IbbHLH3 and IbbHLH4, function antagonistically in activating the IbNAC1 promoter. Notably, IbbHLH3 coordinates activity of IbNAC1 promoter by interaction with several proteins in different time-course of wounding to activate/repress its transcriptional activation function. The dynamic interaction networks of IbbHLH3 improve defense ability against wounding, and timely prevent the injury by IbNAC1-regulated responses.

Previously, the ascorbate peroxidase (APX1) activity and gene expression in Chinese cabbage (Brassica campestris, Bc) heat-tolerant cv. ASVEG2 were found to be significantly higher than in heat-sensitive cv. RN720 under a heat stress. Furthermore, BcAPX2 and BcAPX3, isoforms of BcAPX1, were cloned in this study. Our objective was to transfer BcAPX cDNA under the control of the ubiquitin promoter to Arabidopsis via Agrobacterium tumefaciens strain GV3101. We found that BcAPX genes were overexpressed in transgenic Arabidopsis, and the expression of APX, and the APX activity in transgenic lines were higher than in non-transgenic (NT) plants under high temperatures. The chlorophyll content and the germination rate were significantly higher, and the malondialdehyde content was lower in BcAPX1-3, 2-1, and 3-5 lines subjected to the heat-stress treatment than those in the NT plants. Compared to the NT plants, a lower heat-induced H₂O₂ accumulation was detected by diaminobenzidine staining in leaves of the transgenic lines with a high APX activity indicating that the overexpression of BcAPX in Arabidopsis could enhance heat tolerance by eliminating H₂O₂.