<Emphasis Type="Italic">Catalpa bignonioides</Emphasis> alters extrafloral nectar production after herbivory and attracts ant bodyguards

Inducible anti-herbivore defenses are found within many plant taxa, but there are fewer examples of inducible indirect defenses that incorporate the third trophic level. This study links caterpillar foraging, herbivore-induced changes in extrafloral nectar production, and the attraction of ants to vulnerable leaves and plants. Catalpa bignonioides Walter (Bignoniaceae) uses extrafloral nectar to attract ant (Forelius pruinosus(Roger)) bodyguards in response to Ceratomia catalpae (Boisduval)(Lepidoptera: Sphingidae) herbivory. Ant density per leaf increased with the sugar content of extrafloral nectar excreted by sampled leaves, suggesting that increased nectar production could attract or retain beneficial arthropods. The masses of sucrose, fructose, glucose and all three sugars combined in the extrafloral nectar increased two- to three-fold on attacked leaves within 36 h of the experimental addition of caterpillars. Production rates for neighboring non-attacked leaves and non-attacked leaves on adjacent plants did not differ over the same time period. Ant attendance at caterpillar-attacked leaves increased two- to three-fold within 24 h of herbivory, relative to attendance at neighboring, undamaged leaves. These attacked leaves attracted the fewest ants prior to the onset of herbivory, suggesting the specialist caterpillar may avoid or be excluded from leaves with more bodyguards. The removal of leaf tissue with scissors did not alter ant attendance at damaged leaves. Mean ant attendance per leaf on attacked plants increased 6- to 10-fold after caterpillar introduction, relative to adjacent unattacked plants. The plant's biotic defense thus operates at two scales; the number of bodyguards (ant workers) on the plant increases after attack, and this increased workforce is biased towards attacked leaves within plants. Fewer caterpillars remained on plants that attracted greater numbers of ants, suggesting these bodyguards benefit the plant.     

The chloroplast-localized phospholipases D α4 and α5 regulate herbivore-induced direct and indirect defenses in rice

The oxylipin pathway is of central importance for plant defensive responses. Yet, the first step of the pathway, the liberation of linolenic acid following induction, is poorly understood. Phospholipases D (PLDs) have been hypothesized to mediate this process, but data from Arabidopsis (Arabidopsis thaliana) regarding the role of PLDs in plant resistance have remained controversial. Here, we cloned two chloroplast-localized PLD genes from rice (Oryza sativa), OsPLDα4 and OsPLDα5, both of which were up-regulated in response to feeding by the rice striped stem borer (SSB) Chilo suppressalis, mechanical wounding, and treatment with jasmonic acid (JA). Antisense expression of OsPLDα4 and -α5 (as-pld), which resulted in a 50% reduction of the expression of the two genes, reduced elicited levels of linolenic acid, JA, green leaf volatiles, and ethylene and attenuated the SSB-induced expression of a mitogen-activated protein kinase (OsMPK3), a lipoxygenase (OsHI-LOX), a hydroperoxide lyase (OsHPL3), as well as a 1-aminocyclopropane-1-carboxylic acid synthase (OsACS2). The impaired oxylipin and ethylene signaling in as-pld plants decreased the levels of herbivore-induced trypsin protease inhibitors and volatiles, improved the performance of SSB and the rice brown planthopper Nilaparvata lugens, and reduced the attractiveness of plants to a larval parasitoid of SSB, Apanteles chilonis. The production of trypsin protease inhibitors in as-pld plants could be partially restored by JA, while the resistance to rice brown planthopper and SSB was restored by green leaf volatile application. Our results show that phospholipases function as important components of herbivore-induced direct and indirect defenses in rice.     

一氧化氮与激发子诱导的植物抗病防卫反应

来源于真菌或植物细胞壁的激发子可以诱导植物的抗性反应。一系列的信号分子,如一氧化氮、活性氧、茉莉酸、水杨酸、乙烯等都参与了激发子诱导的植物抗性反应。它们在介导激发子刺激诱发胞内抗性反应的过程中起着重要的作用。本文介绍了激发子的种类,并简述了激发了受体以及植物细胞对激发子刺激的感受与传递;重点介绍了一氧化氮在激发子诱导植物抗性反应过程中的作用,以及它与其他信号分子之间相互关系的研究进展。     

Herbivore-induced plant volatiles mediate host selection by a root herbivore

In response to herbivore attack, plants mobilize chemical defenses and release distinct bouquets of volatiles. Aboveground herbivores are known to use changes in leaf volatile patterns to make foraging decisions, but it remains unclear whether belowground herbivores also use volatiles to select suitable host plants. We therefore investigated how above- and belowground infestation affects the performance of the root feeder Diabrotica virgifera virgifera, and whether the larvae of this specialized beetle are able to use volatile cues to assess from a distance whether a potential host plant is already under herbivore attack. Diabrotica virgifera larvae showed stronger growth on roots previously attacked by conspecific larvae, but performed more poorly on roots of plants whose leaves had been attacked by larvae of the moth Spodoptera littoralis. Fittingly, D. virgifera larvae were attracted to plants that were infested with conspecifics, whereas they avoided plants that were attacked by S. littoralis. We identified (E)-β-caryophyllene, which is induced by D. virgifera, and ethylene, which is suppressed by S. littoralis, as two signals used by D. virgifera larvae to locate plants that are most suitable for their development. Our study demonstrates that soil-dwelling insects can use herbivore-induced changes in root volatile emissions to identify suitable host plants.     

Co(i)-ordinating defenses: NaCOI1 mediates herbivore- induced resistance in Nicotiana attenuata and reveals the role of herbivore movement in avoiding defenses

Arabidopsis and tomato plants mutated in the F-box protein COI1 mediating jasmonate (JA) responses are more susceptible to herbivores in laboratory trials, but the exact mechanisms of COI1-mediated resistance are not known. We silenced COI1 by transformation with an inverted repeat construct (ir-coi1) in Nicotiana attenuata, a plant the direct and indirect defenses of which against various herbivores have been well studied. ir-coi1 plants are male sterile and impaired in JA-elicited direct [nicotine, caffeoylputrescine and trypsin proteinase inhibitor (TPI) activity] and indirect (cis-alpha-bergamotene emission) defense responses; responses not elicited by JA treatment (ethylene production and flower TPI activity) were unaffected. Larvae of Manduca sexta, a common herbivore of N. attenuata, gained three times more mass feeding on ir-coi1 than on wild-type (WT) plants in glasshouse experiments. By regularly moving caterpillars to unattacked leaves of the same plant, we demonstrate that larvae on WT plants can grow and consume leaves as fast as those on ir-coi1 plants, a result that underscores the role of COI1 in mediating locally induced resistance in attacked leaves, and the importance of herbivore movement in avoiding the induced defenses of a plant. When transplanted into native habitats in the Great Basin Desert, ir-coi1 plants suffer greatly from damage by the local herbivore community, which includes herbivores not commonly found on N. attenuata WT plants. Choice assays with field-grown plants confirmed the increased attractiveness of ir-coi1 plants for both common and unusual herbivores. We conclude that NaCOI1 is essential for induced resistance in N. attenuata, and that ir-coi1 plants highlight the benefits of herbivore movement for avoiding induced defenses.     

植物SAR和ISR中的乙烯信号转导网络

乙烯作为重要的信号分子在植物SAR和ISR中发挥重要作用。受病原物和其它激发子处理后,植物体内乙烯被合成,为内质网上一个His激酶类受体家族(Ⅰ型和Ⅱ型)所感知,在铜离子的转运活性下,乙烯与受体的结合使Raf-类Ser/Thr激酶CTR1失活。在CTR1的下游,EIN2、EIN3、EIN5/AIN1、EIN6、EIN7是乙烯反应的正调节子,负责乙烯信号的传导。EIN2编码功能未知的新的膜整合蛋白,而EIN5/AIN1、EIN6和EIN7尚未从分子水平上进行鉴定。定位在核内的DNA结合蛋白EIN3,直接作用于ERF1,调节乙烯反应基因的转录,激活植物防御素和病程相关蛋白基因的表达,使植物建立抗病性反应。