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Summary: 2,4‐Dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one (DIMBOA) and DIMBOA‐glucoside (DIMBOA‐Glc) are anti‐insect benzoxazinoids in maize, yet very little information is known about how they are regulated.Reverse genetics, kinase activity analysis, phytohormone and DIMBOA/DIMBOA‐Glc quantification, bioassays and transcriptome analysis were employed to study the function of ZmMPK6, a mitogen‐activated protein kinase, in maize response to herbivory.ZmMPK6 was rapidly activated by wounding and simulated herbivory. Silencing ZmMPK6 in maize A188 compromised simulated herbivory‐induced ethylene levels but not those of jasmonic acid or salicylic acid, and the ZmMPK6‐silenced plants exhibited elevated DIMBOA/DIMBOA‐Glc and insect resistance. An ethylene complementation experiment revealed that ZmMPK6 repressed the accumulation of DIMBOA/DIMBOA‐Glc in an ethylene‐dependent manner. Transcriptome analysis revealed that ZmMPK6 might meditate the transcription of BX1 by controlling a MYB transcription factor that is likely to be located in the ethylene signalling pathway and, furthermore, ZmMPK6 and ethylene signalling also specifically and commonly regulate the transcription of other benzoxazinoid biosynthetic genes. We also show that different maize lines have very different responses to simulated herbivory in terms of ZmMPK6 activation, ethylene emission and benzoxazinoid levels.These results uncover that ZmMPK6 and ethylene pathway are novel repressors of DIMBOA/DIMBOA‐Glc and provide new insight into the regulatory mechanisms underlying these two pathways. [ABSTRACT FROM AUTHOR]

Summary: Dodders (Cuscuta spp.) are shoot holoparasites, whose haustoria penetrate host tissues to enable fusion between the parasite and host vascular systems, allowing Cuscuta to extract water, nutrients and other molecules from hosts. Aphids are piercing–sucking herbivores that use specialized stylets to feed on phloem sap. Aphids are known to feed on Cuscuta, but how Cuscuta and its host plant respond to aphids attacking the parasite was unknown. Phytohormone quantification, transcriptomic analysis and bioassays were performed to determine the responses of Cuscuta australis and its soybean (Glycine max) hosts to the feeding of green peach aphid (GPA; Myzus persicae) on C. australis. Decreased salicylic acid levels and 172 differentially expressed genes (DEGs) were found in GPA‐attacked C. australis, and the soybean hosts exhibited increased jasmonic acid contents and 1015 DEGs, including > 100 transcription factor genes. Importantly, GPA feeding on C. australis increased the resistance of the soybean host to subsequent feeding by the leafworm Spodoptera litura and soybean aphid Aphis glycines, resulting in 21% decreased leafworm mass and 41% reduced aphid survival rate. These data strongly suggest that GPA feeding on Cuscuta induces a systemic signal, which is translocated to hosts and activates defense against herbivores. [ABSTRACT FROM AUTHOR]

How plants tailor their defense responses to attack from different insects remains largely unknown. Here, we studied the role of a mitogen-activated protein kinase ( MAPK), MPK4, in the resistance of a wild tobacco Nicotiana attenuata to two herbivores, the specialist Manduca sexta and the generalist Spodoptera littoralis., Stably transformed N. attenuata plants silenced in MPK4 (ir MPK4) were generated and characterized for traits important for defense against herbivores., Only the oral secretions ( OS) from M. sexta, but not the OS from S. littoralis or mechanical wounding, induced elevated levels of jasmonic acid ( JA) in ir MPK4 plants relative to the wild-type plants. Moreover, silencing of MPK4 strongly increased the resistance of N. attenuata to M. sexta in a fashion that was independent of COI1 ( CORONATINE INSENSITIVE1)-mediated JA signaling. Untargeted metabolomic screening identified several new MPK4-dependent putative defensive compounds against M. sexta. By contrast, silencing of MPK4 did not affect the growth of the generalist insect S. littoralis, and we propose that this was because of the very low levels of fatty acid-amino acid conjugates ( FACs) in S. littoralis OS., Thus, MPK4 is likely to be a key signaling element that enables plants to tailor defense responses to different attackers. [ABSTRACT FROM AUTHOR]

• Salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) are activated by Manduca sexta attack and elicitors to mediate defense signaling in Nicotiana attenuata. Here, the ecological consequences of SIPK and WIPK silencing for N. attenuata's resistance to M. sexta and its other native herbivores were analyzed. • Stably transformed plants with reduced expression of Na SIPK (irNa SIPK) and Na WIPK(irNa WIPK) were generated and characterized in field and glasshouse experiments. • Both irNa SIPK and irNa WIPK plants had reduced direct and indirect defenses but were not particularly susceptible in nature. In the glasshouse, M. sexta larvae consumed less and gained the same mass on irNa SIPK and irNa WIPK as on wild-type (WT) plants. Green leaf volatile (GLV) emission was highly attenuated in irNa SIPK and irNa WIPK plants, and complementation with synthetic GLVs increased M. sexta performance. To test the hypothesis that reduced GLV emissions account for the lack of herbivory phenotype, GLV emissions were attenuated by silencing Na HPL in jasmonate-deficient plants (asNa LOX3), which are highly susceptible to herbivores. Reducing GLV emissions in asNa LOX3 plants ‘rescued’ these plants from being heavily damaged by M. sexta. • GLV emissions in irNa SIPK and irNa WIPK plants may compensate for the impaired defenses of Na SIPK- and Na WIPK-silenced plants in nature by reducing their apparency to herbivores. [ABSTRACT FROM AUTHOR]

Summary A dodder (Cuscuta) often simultaneously parasitizes two or more adjacent hosts. Phosphate (Pi) deficiency is a common stress for plants, and plants often interact with soil microbes, including arbuscular mycorrhizal fungi (AMF), to cope with Pi stress. Little is known about whether dodder transmits Pi deficiency‐induced systemic signals between different hosts. In this study, dodder‐connected plant clusters, each composed of two tobacco (Nicotiana tabacum) plants connected by a dodder, were established, and in each cluster, one of the two tobacco plants was treated with Pi starvation. AMF colonization efficiency, rhizosphere bacterial community, and transcriptome were analyzed in the other dodder‐connected Pi‐replete tobacco plant to study the functions of interplant Pi signals. We found that dodder transfers Pi starvation‐induced systemic signals between host plants, resulting in enhanced AMF colonization, changes of rhizosphere bacterial communities, and alteration of transcriptomes in the roots of Pi‐replete plants. Importantly, genetic analyses indicated that microRNA399s (miR399s) and strigolactones suppress the systemic Pi signals and negatively affect AMF colonization in the Pi‐replete plants. These findings provide new insight into the ecological role of dodder in mediating host–host and host–microbe interactions and highlight the importance of strigolactone and miR399 pathways in systemic Pi signaling. [ABSTRACT FROM AUTHOR]

• SGT1 (suppressor of G-two allele of SKP1) is a conserved protein in all eukaryotes and is crucial for resisting pathogens in humans and plants. We studied whether SGT1 is involved in the induced defense response of a native tobacco (Nicotiana attenuata) to its natural herbivore, Manduca sexta. • We diminished NaSGT1 transcription in N. attenuata using virus-induced gene silencing (VIGS) and analysed the induced defense responses after wounding and M. sexta elicitation. • Silencing NaSGT1 highly attenuates wounding- and herbivory-induced amounts of jasmonic acid (JA) and JA-isoleucine but elevates the concentration of salicylic acid. Chemical profiling reveals that NaSGT1-silenced plants are also compromised in their ability to accumulate JA precursors produced in chloroplasts. We show that the reduced JA accumulation in NaSGT1-silenced plants is independent of the elevated salicylic acid levels. NaSGT1-silenced plants have decreased contents of defensive metabolites and have compromised resistance to M. sexta larvae. Transcript analyses after methyl jasmonate (MeJA) treatment revealed that NaSGT1 is important for the normal regulation of MeJA-induced transcriptional responses. • This work demonstrates the importance of SGT1 in the regulatory network that deploys defense responses against herbivores, and highlights the significance of SGT1 in plants' responses to JA., (© 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.)