Abstract
Free amino acids in the phloem sap are the dominant nitrogen source for aphids, but their availability is usually poor. Although some studies have explored the effect of dietary amino acid restriction on aphid performance, little is known about the molecular basis of these effects. Here, we examined the performance and transcriptome of the green peach aphid, Myzus persicae, fed a standard diet (Control diet) or a diet containing 50% of the total amino acids of the Control diet (Half diet). Aphid weight and fecundity were significantly reduced in the Half diet group. Transcriptomic analysis showed that a total of 1460 genes were differentially expressed between the groups were fed on the two diets, which many of them were associated with nutrient and energy metabolism. When feeding on the Half diet, aphids upregulated genes associated with the amino acid biosynthetic pathway (predominantly amino acid biosynthesis genes and some amino acid transporter genes) as well as the cysteine and serine protease genes. Furthermore, these aphids displayed increased expression of genes associated with glycolysis, which could generate intermediates for de novo amino acid biosynthesis. Consistent with this, elevated glucose levels were observed in aphids in the Half diet group. Additionally, the expression levels of several genes associated with hormonal signaling pathway were altered. Several genes related to juvenile hormone and insulin-like peptide (ILP) signaling were downregulated, including Krüppel homolog 1 (Kr-h1) and insulin-like peptide 5 (Ilp5), respectively. In contrast, several genes related to ecdysone signaling were upregulated including broad-complex core protein (Br-c) and shade (Shd). Despite their poor performances, M. persicae adapted to dietary restriction of amino acids, through upregulation of genes involved in amino acid biosynthesis, glycolysis, and protein degradation, as well as by altering the expression level of genes involved in hormone signaling pathways.
Highlights
The green peach aphid Myzus persicae, a notorious phloemfeeding hemipteran pest, colonizes more than 400 different plant species from over 50 families (Blackman and Eastop, 2000), and is capable of transmitting more than 100 plant viruses
The restriction of dietary amino acids did not affect the total amount of non-essential amino acids (NEAAs) and essential amino acids (EAAs) (Figure 2A) but significantly affected the amino acid profiles in aphids (Figure 2B)
We found that trehalose, glucose, and sucrose all accumulated at higher concentrations in aphids fed the Half diet compared with the Control diet (Figure 3A)
Summary
The green peach aphid Myzus persicae, a notorious phloemfeeding hemipteran pest, colonizes more than 400 different plant species from over 50 families (Blackman and Eastop, 2000), and is capable of transmitting more than 100 plant viruses. This causes enormous reductions in crop yield, both through direct feeding and by transmission of viruses (Beemster and De Bokx, 1987). Amino acids in plant phloem sap are the dominant dietary nitrogen source for phloem-feeding hemipterans (Ziegler, 1975; Rahbé et al, 1990; Douglas, 1993). The molecular mechanisms underlying the adaptation to dietary restriction of amino acids largely remain unknown
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