Herbivorous insects use diverse feeding strategies to obtain nutrients from their host plants. Rather than acting as passive victims in these interactions, plants respond to herbivory with the production of toxins and defensive proteins that target physiological processes in the insect. Herbivore-challenged plants also emit volatiles that attract insect predators and bolster resistance to future threats. This highly dynamic form of immunity is initiated by the recognition of insect oral secretions and signals from injured plant cells. These initial cues are transmitted within the plant by signal transduction pathways that include calcium ion fluxes, phosphorylation cascades, and, in particular, the jasmonate pathway, which plays a central and conserved role in promoting resistance to a broad spectrum of insects. A detailed understanding of plant immunity to arthropod herbivores will provide new insights into basic mechanisms of chemical communication and plant-animal coevolution and may also facilitate new approaches to crop protection and improvement.

Plant Immunity to Insect Herbivores

The formation and function of plant volatiles: perfumes for pollinator attraction and defense

Polyphenol oxidases in plants and fungi: going places? A review.

Plants have the capacity to synthesize, accumulate and emit volatiles that may act as aroma and flavor molecules due to interactions with human receptors. These low-molecular-weight substances derived from the fatty acid, amino acid and carbohydrate pools constitute a heterogenous group of molecules with saturated and unsaturated, straight-chain, branched-chain and cyclic structures bearing various functional groups (e.g. alcohols, aldehydes, ketones, esters and ethers) and also nitrogen and sulfur. They are commercially important for the food, pharmaceutical, agricultural and chemical industries as flavorants, drugs, pesticides and industrial feedstocks. Due to the low abundance of the volatiles in their plant sources, many of the natural products had been replaced by their synthetic analogues by the end of the last century. However, the foreseeable shortage of the crude oil that is the source for many of the artificial flavors and fragrances has prompted recent interest in understanding the formation of these compounds and engineering their biosynthesis. Although many of the volatile constituents of flavors and aromas have been identified, many of the enzymes and genes involved in their biosynthesis are still not known. However, modification of flavor by genetic engineering is dependent on the knowledge and availability of genes that encode enzymes of key reactions that influence or divert the biosynthetic pathways of plant-derived volatiles. Major progress has resulted from the use of molecular and biochemical techniques, and a large number of genes encoding enzymes of volatile biosynthesis have recently been reported.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2008.03446.x

Biosynthesis of plant-derived flavor compounds.

Tomato ripening is a highly coordinated developmental process that coincides with seed maturation. Regulated expression of thousands of genes controls fruit softening as well as accumulation of pigments, sugars, acids, and volatile compounds that increase attraction to animals. A combination of molecular tools and ripening-affected mutants has permitted researchers to establish a framework for the control of ripening. Tomato is a climacteric fruit, with an absolute requirement for the phytohormone ethylene to ripen. This dependence upon ethylene has established tomato fruit ripening as a model system for study of regulation of its synthesis and perception. In addition, several important ripening mutants, including rin, nor, and Cnr, have provided novel insights into the control of ripening processes. Here, we describe how ethylene and the transcription factors associated with the ripening process fit together into a network controlling ripening.

Genetics and Control of Tomato Fruit Ripening and Quality Attributes

The possibility of communication between plants was proposed nearly 20 years ago, although previous demonstrations have suffered from methodological problems and have not been widely accepted. Here we report the first rigorous, experimental evidence demonstrating that undamaged plants respond to cues released by neighbors to induce higher levels of resistance against herbivores in nature. Sagebrush plants that were clipped in the field released a pulse of an epimer of methyl jasmonate that has been shown to be a volatile signal capable of inducing resistance in wild tobacco. Wild tobacco plants with clipped sagebrush neighbors had increased levels of the putative defensive oxidative enzyme, polyphenol oxidase, relative to control tobacco plants with unclipped sagebrush neighbors. Tobacco plants near clipped sagebrush experienced greatly reduced levels of leaf damage by grasshoppers and cutworms during three field seasons compared to unclipped controls. This result was not caused by an altered light regime experienced by tobacco near clipped neighbors. Barriers to soil contact between tobacco and sagebrush did not reduce the difference in leaf damage although barriers that blocked air contact negated the effect.

Communication between plants : induced resistance in wild tobacco plants following clipping of neighboring sagebrush

Plant Volatile Compounds: Sensory Cues for Health and Nutritional Value?

Methyl jasmonate is blowing in the wind, but can it act as a plant-plant airborne signal?

Nicotiana repanda Wildenow ex Lehmann acylates nornicotine in its trichomes to produce N-acyl-nornicotine (NacNN) alkaloids which are dramatically more toxic than nicotine is to the nicotine-adapted herbivore, Manduca sexta. These NacNNs, like nicotine, were induced by methyl jasmonate (MeJA) and wounding, but the 2-fold increase in NacNN pools was much faster (within 6 h) than the MeJA-induced increase in nornicotine pools (24 h to 4 d), its parent substrate. When 15NO3
− pulse-chase experiments with intact and induced plants were used to follow the incorporation of 15N into alkaloids in different plant parts over the plant's lifetime, it was found that the root nicotine pool was most rapidly labeled, followed by the shoot nornicotine and NacNN pools. After 3 d, 3.12% of 15N acquired was in nicotine (0.93%), nornicotine (0.32%) and NacNNs (1.73%) while only 0.14% was in anabasine. Once NacNNs are externalized to the leaf surface, they are not readily re-distributed within the plant and are lost with senescing leaves. The wound- and MeJA-induced N-acylation of nornicotine is independent of induced changes in nornicotine pools and the rapidity of the response suggests its importance in defense against herbivores.

Fast track to the trichome: induction of N-acyl nornicotines precedes nicotine induction in Nicotiana repanda.

Nicotiana attenuata plants growing in close proximity to damaged sagebrush (Artemisia tridentata ssp tridentata) suffer less herbivory than plants near undamaged sagebrush Sagebrush constitutively releases methyl jasmonate (MeJA), a compound that when applied directly to N attenuata, elicits herbivore resistance and the direct defense traits [protease inhibitors (PIs), nicotine] Damage increases the release of volatile MeJA, primarily in the cis epimer, suggesting that cis-MeJA may mediate this apparent interplant signaling We characterized sagebrush's MeJA plume before and after damage in nature and in the laboratory, and compared the activity of trans- and cis-MeJA in inducing PIs, nicotine, and Manduca sexta resistance in N attenuata We used both lanolin applications and aqueous sprays that mimic natural exposures, and we determined the amount of volatilized MeJA required to elicit a nicotine response in open-grown plants Wounding rapidly and transiently increased cis-MeJA emissions from damaged parts (but not systemically), and the released plume did not rapidly dissipate in nature cis-MeJA was not consistently more active than trans-MeJA, and the order of exposure (trans- then cis-) did not influence activity We conclude that volatile MeJA, either trans- or cis-, when applied at levels consistent with those released by sagebrush does not elicit direct defenses in N attenuata

Plant-plant signaling: application of trans- or cis-methyl jasmonate equivalent to sagebrush releases does not elicit direct defenses in native tobacco.

Grit Laue

Papers

Communication between plants : induced resistance in wild tobacco plants following clipping of neighboring sagebrush

Plant Volatile Compounds: Sensory Cues for Health and Nutritional Value?

Methyl jasmonate is blowing in the wind, but can it act as a plant-plant airborne signal?

Fast track to the trichome: induction of N-acyl nornicotines precedes nicotine induction in Nicotiana repanda.

Plant-plant signaling: application of trans- or cis-methyl jasmonate equivalent to sagebrush releases does not elicit direct defenses in native tobacco.