The analysis of large-scale gene expression correlated to the phase changes of the migratory locust

Abstract

The migratory locust is one of the most notorious agricultural pests that undergo a well known reversible, density-dependent phase transition from the solitary to the gregarious. To demonstrate the underlying molecular mechanisms of the phase change, we generated 76,012 ESTs from the whole body and dissected organs in the two phases. Comparing 12,161 unigene clusters, we identified 532 genes as phase-related (P < 0.01). Comprehensive assessment of the phase-related expression revealed that, whereas most of the genes in various categories from hind legs and the midgut are down-regulated in the gregarious phase, several gene classes in the head are impressively up-regulated, including those with peptidase, receptor, and oxygen-binding activities and those related to development, cell growth, and responses to external stimuli. Among them, a superfamily of proteins, the JHPH super-family, which includes juvenile hormone-binding protein, hexamerins, prophenoloxidase, and hemocyanins, were highly expressed in the heads of the gregarious hoppers and hind legs of the solitary hoppers. Quantitative PCR experiments confirmed in part the EST results. These differentially regulated genes have strong functional implications that numerous molecular activities are involved in phase plasticity. This study provides ample molecular markers and genomic information on hemimetabolous insects and insights into the genetic and molecular mechanisms of phase changes in locusts.

Fig. 1.

The distribution of annotated unigenes based on publicly available databases (D. melanogaster and B. mori) by blastx. Homology was estimated based on different E values, <1e-5 (A) and <1e-10 (B). Genomic data from B. mori are also included (Q. Xia and J.Y., unpublished data).

Fig. 2.

go classification of genes differentially expressed (P < 0.01) in the head (A), hind legs (B) and midgut (C) of solitary and gregarious locusts. Categories having fewer than three unigene clusters are not included. In the go functional categories, -a, -b, and -m stand for activity, binding, and metabolism, respectively.

Fig. 3.

Representative Q-PCR results from selected unigenes. Differentially expressed unigenes discovered in EST survey in solitary and gregarious phases from the head (A) and hind-leg (B) libraries were validated experimentally. Expression levels were normalized as relative abundance (y axis). Scales over the bar graph indicate SEs. Asterisks on the top of each bar highlight the significance levels of the individual experiments (*, P < 0.05; **, P < 0.01). Unfilled bars and filled bars denote the expression levels of the solitary (S) and gregarious (G) phases, respectively. The abbreviations in the chart and unigenes used in the experiment are as follows: LCP-17, larval cuticle protein LCP-17 precursor (LMC_004183); NIPK, neuronal cell death inducible putative kinase (LMC_001295); ATPsyn-b, F-type ATPase complex β subunit (LMC_002337); AM, ATP-binding myosin (LMC_002592); TF, transcription factor (LMC_004015); JHPH2, member of JHPH2 family (LMC_002189); NaDg, β-N-acetylhexosaminidase activity (LMC_003978); Rag1, recombination activating gene 1 (LMC_000750); MSM, microtubule structural molecule activity (LMC_004292); CCO3, cytochrome c oxidase chain 3 (LMC_001579); troponin C (LMC_001149); LCPP, larval cuticle protein precursor (LMC_002346); AS, similar to asparagine synthetase (LMC_002788); AF, actin filament components (LMC_000202); FAE, putative fatty acid elongase (LMC_000202); AC1, similar to brain adenylate cyclase 1(LMC_001410); ZFX, similar to sex-determining protein Zfx (LMC_001624); annexin IX (LMC_002984); and NADP-ME, NADP-dependent malic enzyme (LMC_003913).