Increased cysteine protease activity in the aphid midgut decreases the transmission efficiency of a circulative plant virus

ABSTRACT: Aphids, sap-sucking insects in the order Hemiptera, are among the most prolific insect vectors of plant viruses Plant viruses from the family Luteoviridae are transmitted exclusively by aphids in a circulative manner and cause significant crop yield losses. Circulative plant viruses must cross the aphid gut and other tissues prior to transmission to a new host plant. The discovery of proteins that control acquisition and transmission in the insect vector is the biggest challenge for the vector biology field and will have practical applications for growers by providing new molecular targets for the development of precision vector management tools. The green peach aphid, Myzus persicae, is a vector of the Potato leafroll virus (PLRV), a polerovirus in the Luteoviridae. PLRV transmission efficiency was significantly reduced when a clonal lineage of M. persicae was reared on turnip (T-Myzus) as compared to the weed physalis (P-Myzus). The effect on PLRV transmission efficiency was transient and caused by a host-switch response. Using 2-D DIGE, we revealed that the major difference in the proteome profile of P- and T-Myzus was the lysosomal cysteine protease cathepsin B, with multiple size and charge isoforms of this enzyme up-regulated in T-Myzus. Quantitative, shotgun proteomics revealed a specific upregulation in the expression of other lysosomal proteins in T-Myzus as compared to P-Myzus, including cathepsin B, cathepsin B-16, beta-glucuronidase, peroxidasin, legumain-like, and aminopeptidase-N. The titer of PLRV was over 1.5 fold higher in P-Myzus than in T-Myzus at 24h and 72h after the beginning of virus acquisition, suggesting that virus acquisition in P-Myzus was more efficient. Cathepsin B and PLRV localization were starkly different in P- and T-Myzus midguts, the site of PLRV acquisition into the insect. In P-Myzus midguts, an abundance of PLRV was observed inside midgut cells, and cathepsin B was sequestered in a subcellular compartment. In contrast, there is near complete co-localization of cathepsin B and PLRV at the cell membranes in viruliferous T-Myzus. Inhibition of cathepsin and other cysteine proteases with E64 restored the ability of T-Myzus to transmit PLRV in a dose-dependent manner, suggesting that the activities of lysosomal cysteine proteases at the cell membrane in T-Myzus is responsible for the change in virus transmission phenotype in these aphids. T-Myzus individuals weighed more and had more progeny than P-Myzus individuals. These data are all consistent with the hypothesis that there is an induction of lysosomal exocytos in the midgut of T-Myzus linked to the ability of the aphid to acquire PLRV. These data also show that the ability of the generalist aphid M. persicae to transmit PLRV is influenced by the host plant the aphids are reared on, information that is useful to growers for polerovirus management in field crops.

INSTRUMENT(S): TSQ Vantage, Q Exactive

ORGANISM(S): Myzus Persicae Persicae

TISSUE(S): Whole Body

SUBMITTER: Kevin Howe  

LAB HEAD: Michelle Cilia

PROVIDER: PXD004893 | Pride | 2016-12-14

REPOSITORIES: Pride