This strategy also poses high risks to crops by distant transmission of viral diseases vectored by aphids. Thus, it is important to understand how aphids perceive environmental cues in triggering wing dimorphism and exploit specific approaches to target this process. Here, we report a microRNA (miR-9b)-mediated signal cascade that controls high-population-density–induced wing dimorphism in aphids. This finding highlights that small RNAs are important in regulating signal transduction of insect phenotypic plasticity when insects face environmental challenges, which may provide an alternative for the development of dispersal restriction-based pest control.
Wing dimorphism is a phenomenon of phenotypic plasticity in aphid dispersal. However, the signal transduction for perceiving environmental cues (e.g., crowding) and the regulation mechanism remain elusive. Here, we found that aci-miR-9b was the only down-regulated microRNA (miRNA) in both crowding-induced wing dimorphism and during wing development in the brown citrus aphid Aphis citricidus. We determined a targeted regulatory relationship between aci-miR-9b and an ABC transporter (AcABCG4). Inhibition of aci-miR-9b increased the proportion of winged offspring under normal conditions. Overexpression of aci-miR-9b resulted in decline of the proportion of winged offspring under crowding conditions. In addition, overexpression of aci-miR-9b also resulted in malformed wings during wing development. This role of aci-miR-9b mediating wing dimorphism and development was also confirmed in the pea aphid Acyrthosiphon pisum. The downstream action of aci-miR-9b-AcABCG4 was based on the interaction with the insulin and insulin-like signaling pathway. A model for aphid wing dimorphism and development was demonstrated as the following: maternal aphids experience crowding, which results in the decrease of aci-miR-9b. This is followed by the increase of ABCG4, which then activates the insulin and insulin-like signaling pathway, thereby causing a high proportion of winged offspring. Later, the same cascade, “miR-9b-ABCG4-insulin signaling,” is again involved in wing development. Taken together, our results reveal that a signal transduction cascade mediates both wing dimorphism and development in aphids via miRNA. These findings would be useful in developing potential strategies for blocking the aphid dispersal and reducing viral transmission.
Figure 1: RNA-seq reveals that aci-miR-9b is involved in wing dimorphism and wing development in A. citricidus. (A) The proportion of winged offspring under crowding. normal, 10 adults in a stem-leaf device; crowding, 80 adults in a stem-leaf device. Mean (±SE) is based on four biological replicates. The significant difference between crowding and normal is indicated by asterisks (***P < 0.001). (B) Schematic diagram of wing dimorphism and wing development and strategy for RNA-seq in A. citricidus. The red triangles represent the location of the wing (wing bud) in winged morphs. The comparisons inside the dashed box indicate the strategy of RNA-seq. Red-dashed boxes indicate the potential miRNAs mediating wing dimorphism (normal vs. crowding) and wing development (N4-WD vs. AD-WD) while the blue-dashed box is used to exclude the miRNAs in aphid development but not specifically for wing development (N4-WL vs. AD-WL). (C) The differentially expressed miRNAs among crowding vs. normal, AD-WD vs. N4-WD, and AD-WL vs. N4-WL. miRNAs with an adjusted P value < 0.01 and the absolute value of a fold change > 1.25 found by DESeq were assigned as differentially expressed. In each comparison, the relative expression of miRNAs was clustered based on z-scores from low to high value (with a scale from −1 to 1) among all of the biological replicates. Up-regulation is represented by red shading and down-regulation is represented by blue shading. R1 to R4 represent biological replicates; normal, wingless adult under normal condition; crowding, wingless adult under crowding; N1, first instar nymph; N2, second instar nymph; N3-WD, third instar winged nymph; N3-WL, third instar wingless nymph; N4-WD, fourth instar winged nymph; N4-WL, fourth instar wingless nymph; AD-WD, winged adult; AD-WL, wingless adult.