Plants respond to herbivore attack with a dramatic functional reorganization that involves the activation of direct and indirect defenses and tolerance, which in turn make large demands on primary metabolism. Here we provide the first characterization of the transcriptional reorganization that occurs after insect attack in a model plant-herbivore system: Nicotiana attenuata Torr. ex Wats.-Manduca sexta. We used mRNA differential display to characterize one-twentieth of the insect-responsive transcriptome of N. attenuata and verified differential expression for 27 cDNAs. Northern analyses were used to study the effects of folivory and exposure to airborne methyl jasmonate and for kinetic analyses throughout a 16-hlight/8-h-dark cycle. Sequence similarity searches allowed putative functions to be assigned to 15 transcripts. Genes were related to photosynthesis, electron transport, cytoskeleton, carbon and nitrogen metabolism, signaling, and a group responding to stress, wounding, or invasion of pathogens. Overall, transcripts involved in photosynthesis were strongly down-regulated, whereas those responding to stress, wounding, and pathogens and involved in shifting carbon and nitrogen to defense were strongly up-regulated. The majority of transcripts responded similarly to airborne methyl jasmonate and folivory, and had tissue-and diurnal-specific patterns of expression. Transcripts encoding Thr deaminase (TD) and a putative retrotransposon were absent in control plants, but were strongly induced after herbivory. Full-length sequences were obtained for TD and the pathogen-inducible ␣-dioxygenase, PIOX. Effects of abiotic and biotic stimuli were investigated for transcripts encoding TD, importin ␣, PIOX, and a GAL83-like kinase cofactor.

The transcriptional changes in Nicotiana attenuata Torr. ex Wats. elicited by attack from Manduca sexta larvae were previously characterized by mRNA differential display (D. Hermsmeier, U. Schittko, I.T. Baldwin [2001] Plant Physiol 125: 683-700). Because herbivore attack causes wounding, we disentangled wound-induced changes from those elicited by M. sexta oral secretions and regurgitant (R) with a northern analysis of a subset of the differentially expressed transcripts encoding threonine deaminase, pathogen-induced oxygenase, a photosystem II light-harvesting protein, a retrotransposon homolog, and three unknown genes. R extensively modified wound-induced responses by suppressing wound-induced transcripts (type I) or amplifying the wound-induced response (type II) further down-regulating wound-suppressed transcripts (type IIa) or up-regulating wound-induced transcripts (type IIb). It is interesting that although all seven genes displayed their R-specific patterns in the treated tissues largely independently of the leaf or plant developmental stage, only the type I genes displayed strong systemic induction. Ethylene was not responsible for any of the specific patterns of expression. R collected from different tobacco feeding insects, M. sexta, Manduca quinquemaculata, and Heliothis virescens, as well as from different instars of M. sexta were equally active. The active components of M. sexta R were heat stable and active in minute amounts, comparable with real transfer rates during larval feeding. Specific expression patterns may indicate that the plant is adjusting its wound response to efficiently fend off M. sexta, but may also be advantageous to the larvae, especially when R suppress wound-induced plant responses.

The marked cellular changes during feeding site formation of the soybean cyst nematode (Heterodera glycines) indicate major changes in soybean gene expression. We used differential display of mRNA to detect host gene expression changes during the early compatible interaction between soybean and H. glycines. Fifteen cDNA clones corresponding to mRNAs with different abundances in H. glycines-infected versus uninfected roots were identified. Differential display results indicated that abundances of five mRNAs increased in infected roots, whereas abundances of 10 mRNAs decreased. Transcripts for nine of these 15 cDNAs could be detected on RNA blots, and their hybridization signals confirmed the differential display results for eight of these nine cDNAs. Sequence analyses identified five cDNAs with decreased mRNA levels in infected roots as corresponding to two putative aldolase genes, a transcription-factor TFIIA homologue, the soybean small GTP-binding protein gene sra1, and the soybean auxin down-regulated gene ADR12. RNA blot analyses of other auxin down-regulated genes revealed a decrease in their mRNA abundances in H. glycines-infected roots as well.

Gene expression changes in plant roots infected by plant-parasitic cyst nematodes are involved in the formation of nematode feeding sites. We analyzed mRNA abundance changes within roots of Arabidopsis thaliana during the early compatible interaction with Heterodera schachtii, the sugarbeet cyst nematode. Approximately 1,600 root sections, each containing a single parasitic nematode and its feeding site, and 1,600 adjacent, nematode-free root sections were excised from aseptic A. thaliana cultures 3 to 4 days after inoculation with H. schachtii. These tissue samples were termed infected and uninfected, respectively. Preparasitic nematodes were added to the uninfected tissue sample to maintain the nematode to plant tissue proportion. mRNA extracted from these two tissue samples was subjected to differential display analysis. Thirty-six cDNA clones corresponding to mRNA species with different abundance between both tissue samples were isolated. Of these clones, 24 were of A. thaliana origin and 12 were from H. schachtii. Differential display data predicted that the A. thaliana cDNA clones corresponded to 13 transcripts that were more abundant in the infected root sections and 11 transcripts that were more abundant in the uninfected root sections. H. schachtii cDNA clones were predicted to correspond to four transcripts that were more abundant in parasitic nematodes and to eight transcripts that were more abundant in preparasitic nematodes. In situ hybridization experiments confirmed the mRNA abundance changes in A. thaliana roots predicted by the differential display analyses for two A. thaliana clones.

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The unicellular green alga Scenedesmus obliquus adapts to different irradiances and wavelengths of light by altering the molecular organization of the photosynthetic apparatus. Regulation occurs on the level of pigment-accumulation, assembly of pigmentprotein complexes and gene-expression. Action spectroscopy revealed the involvement of at least two photoreceptor-systems regulating adaptation antagonistically with markedly different thresholds (Thielmann et ai., 1991;. One of them was a BL-(flavin-type-) receptor, which mediates weak-light adaptation, resulting in increased Chi, LHC II (Humbeck et ai., 1988;Senger and Bauer, 1987) and accumulation of cab-mRNA (Hermsmeier et ai., 1991); the other one was a VL/RL-receptor with action peaks at 404 and 650 nm, inducing high-irradiance responses indicated by decreased amounts of Chi, LHC II, LHCP and cab-mRNA (Hermsmeier et ai., 1991).

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The patterns of accumulation of photosynthetic