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Differential transcript accumulation in seedling and mature shoots identifies components contributing to corn earworm resistance

ABSTRACT: As maize seedlings germinate into the soil, they encounter an environment teeming with insects seeking rich sources of nutrition. Maize presumably has developed a number of molecular mechanisms to ensure survival at the beginning of its life cycle. Bioassays indicated maize seedlings were more toxic to caterpillars than shoots from 3 or 4 leafed plants. Microarray technology was utilized to document the expression of a number of genes with potential defensive functions in seedling tissue. In addition to elevated levels of the genes involved in the biosynthesis of DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), an anti-insect resistance molecule, other highly expressed genes in the seedling encode the following putative proteins: defensin, hydroxyproline and proline-rich protein, thaumatin-like protein, lipase, cystatin, protease inhibitor, and a variety of proteases. Changes in the levels of gene expression by the microarray technology were well correlated to results using quantitative RT-PCR. The potential resistance genes identified occurred mainly on chromosomes 1 and 5 in the B73 genome. Analysis of promoters of four DIMBOA biosynthetic genes determined that a Dof transcription factor, two of which were differentially expressed in three vegetative stages, is possibly involved in regulation of the DIMBOA biosynthetic pathway. The results indicate that maize employs a wide variety of potential resistance mechanisms in seedling tissue to resist a possible insect attack.

ORGANISM(S): Zea mays

PROVIDER: GSE27709 | GEO | 2011/11/03

SECONDARY ACCESSION(S): PRJNA138117

REPOSITORIES: GEO

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Project description:As maize seedlings germinate into the soil, they encounter an environment teeming with insects seeking rich sources of nutrition. Maize presumably has developed a number of molecular mechanisms to ensure survival at the beginning of its life cycle. Bioassays indicated maize seedlings were more toxic to caterpillars than shoots from 3 or 4 leafed plants. Microarray technology was utilized to document the expression of a number of genes with potential defensive functions in seedling tissue. In addition to elevated levels of the genes involved in the biosynthesis of DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), an anti-insect resistance molecule, other highly expressed genes in the seedling encode the following putative proteins: defensin, hydroxyproline and proline-rich protein, thaumatin-like protein, lipase, cystatin, protease inhibitor, and a variety of proteases. Changes in the levels of gene expression by the microarray technology were well correlated to results using quantitative RT-PCR. The potential resistance genes identified occurred mainly on chromosomes 1 and 5 in the B73 genome. Analysis of promoters of four DIMBOA biosynthetic genes determined that a Dof transcription factor, two of which were differentially expressed in three vegetative stages, is possibly involved in regulation of the DIMBOA biosynthetic pathway. The results indicate that maize employs a wide variety of potential resistance mechanisms in seedling tissue to resist a possible insect attack. Three different Zea mays plant (B73) life stages were sampled: a) seedlings, which had grown just above the soil line, which also served as reference tissue (reference tissue was always labeled Cy5 and consisted of leaf shoots pooled from 12 plants); b) leaf shoots from plants with four leaves; and c) leaf shoots from plants with six leaves. There were 3 samples (biological replications) of each treatment (6 plants per sample) and the samples were labeled Cy3 and which were combined with a reference chip for a total of 9 chips: (3 biological replicates of seedling, 4 leaf stage and 6 leaf stage).

Project description:Arabidopsis thaliana plants were infested i) with sucking insect herbivores (the generalist aphid Myzus persicae and the specialist aphid Brevicoryne brassicae), ii) with chewing insect herbivores (generalist caterpillars of Spodoptera exigua and specialist caterpillars of Pieris rapae) or iii) were treated by wounding. For each treatment, rosette leaves were harvested at two time points (6h and 24h) after removal of insects. For chewing herbivores and wounding both local, i.e. immediately damaged leaves, and systemic, i.e. undamaged leaves from the same plant, were collected. Control plants were uninfested, but otherwise equally treated and harvested in parallel. We tested the hypothesis that Arabidopsis can recognize and respond differentially to insect species at the transcriptional level using a genome wide microarray. Transcriptional reprogramming was characterized using co-expression analysis in damaged and undamaged leaves at two times in response to mechanical wounding and four insect species. In all, 2778 (10.6%) of annotated genes on the array were differentially expressed in at least one treatment. Responses differed mainly between aphid and caterpillar and sampling times. Responses to aphids and caterpillars shared only 10% of up-regulated and 8% of down-regulated genes. Responses to two caterpillars shared 21% and 12% of up- and down-regulated genes, whereas responses to the two aphids shared only 7% and 4% of up-regulated and down-regulated genes. Overlap in genes expressed between 6h and 24h was 3-15%, and depended on the insect species. Responses in attacked and unattacked leaves differed at 6h but converged by 24h. Genes responding to the insects are also responsive to many stressors and included primary metabolism. Aphids down-regulated amino acid catabolism; caterpillars stimulated production of amino acids involved in glucosinolate synthesis. Co-expression analysis revealed 17 response networks. Transcription factors were a major portion of differentially expressed genes throughout and responsive genes shared most of the known or postulated binding sites.

Project description:Native host plant insect resistance in the maize inbred line Mp708 was developed by traditional plant breeding. Resistant Mp708 thwarts feeding by fall armyworm (Spodoptera frugiperda [J.E. Smith]; Lepidoptera: Noctuidae), numerous other lepidopteran pests, and the coleopteran western corn rootworm. This broad resistance makes it an excellent model for studying native host plant resistance mechanisms. In response to caterpillar feeding, Mp708 rapidly mobilizes Mir1-CP, a unique cysteine protease that appears to translocate from roots to the maize midwhorl where it accumulates. This accumulation correlates with a significant reduction in caterpillar growth resulting from diminished food utilization. In addition, the peritrophic membrane (PM) that surrounds the food bolus in the mudgut (MG) is severely damaged in caterpillars fed on sweet corn callus transformed to express the gene encoding Mir1-CP or on midwhorl tissue from resistant Mp708 maize. Functions of the PM include assisting digestion and protecting the epithelium of the caterpillar MG from physical and chemical damage. Consequently, the reduced growth of caterpillars that feed on Mp708 is probably due to the action of Mir1-CP on PM physiology. In fact, previous in vitro studies indicated that Mir1-CP was capable of permeabilizing the PM. The present study used both targeted (qRT-PCR) and global (mRNA-seq) transcriptome analyses to explore the effect of eating Mir1-CP expressing Mp708 maize on abundance of transcripts in the MG of fall armyworm larvae in comparison to MGs from larvae fed on susceptible Tx601 maize that does not express Mir1-CP. Expression of genes encoding proteins involved in PM production is upregulated in MGs from fall armyworm fed on Mp708. Also, several digestive enzymes (endopeptidases, aminopeptidases, lipases, amylase) were more highly expressed in MGs from larvae fed on Mp708 than MGs from larvae fed on Tx601. Impaired growth of larvae fed on Mp708 probably results from metabolic costs associated with higher production of PM constituents and digestive enzymes in a compensatory attempt to maintain MG function.

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Differential transcript accumulation in seedling and mature shoots identifies components contributing to corn earworm resistance

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