When attacked by a phloem-feeding greenbug aphid (Schizaphis graminum), sorghum (Sorghum bicolor) activates jasmonic acid (JA)- and salicylic acid (SA)-regulated genes, as well as genes outside known wounding and SA signaling pathways. A collection of 672 cDNAs was obtained by differential subtraction with cDNAs prepared from sorghum seedlings infested by greenbug aphids and those from uninfested seedlings. Subsequent expression profiling using DNA microarray and northern-blot analyses identified 82 transcript types from this collection responsive to greenbug feeding, methyl jasmonate (MeJA), or SA application. DNA sequencing analyses indicated that these encoded proteins functioning in direct defense, defense signaling, oxidative burst, secondary metabolism, abiotic stress, cell maintenance, and photosynthesis, as well as proteins of unknown function. In response to insect feeding, sorghum increased transcript abundance of numerous defense genes, with some SA-dependent pathogenesis-related genes responding to greenbug more strongly than to SA. In contrast, only weak induction of MeJA-regulated defense genes was observed after greenbug treatment. However, infestation tests confirmed that JA-regulated pathways were effective in plant defense against greenbugs. Activation of certain transcripts exclusively by greenbug infestation was observed, and may represent unique signal transduction events independent of JA- and SA-regulated pathways. Results indicate that plants coordinately regulate defense gene expression when attacked by phloem-feeding aphids, but also suggest that aphids are able to avoid triggering activation of some otherwise potentially effective plant defensive machinery, possibly through their particular mode of feeding.

Although the function of silicon (Si) in plant physiology has long been debated, its beneficial effects on plant resistance against abiotic and biotic stresses, including insect herbivory, have been well documented. In addition, the jasmonate (JA) signaling pathway plays a crucial role in mediating antiherbivore defense responses in plants. However, potential interactions between JA and Si in response to insect attack have not been examined directly. To explore the role JA may play in Si-enhanced resistance, we silenced the expression of allene oxide synthase (OsAOS; active in JA biosynthesis) and CORONATINE INSENSITIVE1 (OsCOI1; active in JA perception) genes in transgenic rice plants via RNAi and examined resulting changes in Si accumulation and defense responses against caterpillar Cnaphalocrocis medinalis (rice leaffolder, LF) infestation. Si pretreatment increased rice resistance against LF larvae in wild-type plants but not in OsAOS and OsCOI1 RNAi lines. Upon LF attack, wild-type plants subjected to Si pretreatment exhibited enhanced defense responses relative to untreated controls, including higher levels of JA accumulation; increased levels of transcripts encoding defense marker genes; and elevated activities of peroxidase, polyphenol oxidase, and trypsin protease inhibitor. Additionally, reduced Si deposition and Si cell expansion were observed in leaves of OsAOS and OsCOI1 RNAi plants in comparison with wild-type plants, and reduced steady-state transcript levels of the Si transporters OsLsi1, OsLsi2, and OsLsi6 were observed in Si-pretreated plants after LF attack. These results suggest a strong interaction between Si and JA in defense against insect herbivores involving priming of JA-mediated defense responses by Si and the promotion of Si accumulation by JA.Oryza sativa | induced defense | jasmonic acid | mitogen-activated protein kinase

Human utilization of the mulberry–silkworm interaction started at least 5,000 years ago and greatly influenced world history through the Silk Road. Complementing the silkworm genome sequence, here we describe the genome of a mulberry species Morus notabilis. In the 330-Mb genome assembly, we identify 128 Mb of repetitive sequences and 29,338 genes, 60.8% of which are supported by transcriptome sequencing. Mulberry gene sequences appear to evolve ~3 times faster than other Rosales, perhaps facilitating the species’ spread worldwide. The mulberry tree is among a few eudicots but several Rosales that have not preserved genome duplications in more than 100 million years; however, a neopolyploid series found in the mulberry tree and several others suggest that new duplications may confer benefits. Five predicted mulberry miRNAs are found in the haemolymph and silk glands of the silkworm, suggesting interactions at molecular levels in the plant–herbivore relationship. The identification and analyses of mulberry genes involved in diversifying selection, resistance and protease inhibitor expressed in the laticifers will accelerate the improvement of mulberry plants.

The soybean cysteine protease inhibitor, soyacystatin N (scN), negatively impacts growth and development of the cowpea bruchid, Callosobruchus maculatus[Koiwa et al. (1998) Plant J 14: 371-379]. However, the developmental delay and feeding inhibition caused by dietary scN occurred only during the early developmental stages (the 1st, 2nd and 3rd instars) of the cowpea bruchid. The 4th instar larvae reared on scN diet (adapted) exhibited rates of feeding and development which were comparable to those feeding on an scN-free diet (unadapted) prior to pupation. Total gut proteolytic capacity at this larval stage significantly increased in the scN-adapted insects. The elevated enzymatic activity was attributed to a differential expression of insect gut cysteine proteases (representing the major digestive enzymes), and of aspartic proteases. scN degradation by the gut extract was observed only in adapted bruchids, and this activity appeared to be a combined effect of scN-induced cysteine and aspartic proteases. Thirty cDNAs encoding cathepsin L-like cysteine proteases were isolated from insect guts, and they were differentially regulated by dietary scN. Our results suggest that the cowpea bruchid adapts to the challenge of scN by qualitative and quantitative remodelling of its digestive protease complement, and by activating scN-degrading protease activity.

Plant protease inhibitors (PIs) are natural plant defense proteins that inhibit proteases of invading insect herbivores. However, their anti-insect efficacy is determined not only by their potency toward a vulnerable insect system but also by the response of the insect to such a challenge. Through the long history of coevolution with their host plants, insects have developed sophisticated mechanisms to circumvent antinutritional effects of dietary challenges. Their response takes the form of changes in gene expression and the protein repertoire in cells lining the alimentary tract, the first line of defense. Research in insect digestive proteases has revealed the crucial roles they play in insect adaptation to plant PIs and has brought about a new appreciation of how phytophagous insects employ this group of molecules in both protein digestion and counterdefense. This review provides researchers in related fields an up-to-date summary of recent advances.

Indirect evidence previously suggested that Arabidopsis (Arabidopsis thaliana) vegetative storage protein (VSP) could play a role in defense against herbivorous insects. To test this hypothesis, other AtVSP-like sequences in Arabidopsis were identified through a Basic Local Alignment Search Tool search, and their transcriptional profiles were investigated. In response to methyl jasmonate application or phosphate starvation, AtVSP and AtVSP-like genes exhibited differential expression patterns, suggesting distinct roles played by each member. Arabidopsis VSP2 (AtVSP2), a gene induced by wounding, methyl jasmonate, insect feeding, and phosphate deprivation, was selected for bacterial expression and functional characterization. The recombinant protein exhibited a divalent cation-dependent phosphatase activity in the acid pH range. When incorporated into the diets of three coleopteran and dipteran insects that have acidic gut lumen, recombinant AtVSP2 significantly delayed development of the insects and increased their mortality. To further determine the biochemical basis of the anti-insect activity of the protein, the nucleophilic aspartic acid-119 residue at the conserved DXDXT signature motif was substituted by glutamic acid via site-directed mutagenesis. This single-amino acid alteration did not compromise the protein's secondary or tertiary structure, but resulted in complete loss of its acid phosphatase activity as well as its anti-insect activity. Collectively, we conclude that AtVSP2 is an anti-insect protein and that its defense function is correlated with its acid phosphatase activity.

Feeding bioassay results established that the soybean cysteine proteinase inhibitor N (soyacystatin N, scN) substantially inhibits growth and development of western corn rootworm (WCR), by attenuating digestive proteolysis [Zhao, Y. et al. (1996. Recombinant scN was more inhibitory than the potent and broad specificity cysteine proteinase inhibitor E-64. WCR digestive proteolytic activity was separated by mildly denaturing SDS^PAGE into two fractions and in-gel assays confirmed that the proteinase activities of each were largely scN-sensitive. Since binding affinity to the target proteinase [Koiwa, H. et al. (1998) Plant J. 14, 371^380] governs the effectiveness of scN as a proteinase inhibitor and an insecticide, five peptides (28^33 kDa) were isolated from WCR gut extracts by scN affinity chromatographic separation. Analysis of the N-terminal sequence of these peptides revealed similarity to a cathepsin L-like cysteine proteinase (DvCAL1, Diabrotica virgifera virgifera cathepsin L) encoded by a WCR cDNA. Our results indicate that cathepsin L orthologs are pivotal digestive proteinases of WCR larvae, and are targets of plant defensive cystatins (phytocystatins), like scN.z 2000 Federation of European Biochemical Societies.

No abstract