A New Barley Stripe Mosaic Virus Allows Large Protein Overexpression for Rapid Function Analysis

Understanding genetic and molecular bases of gene function is of increasing importance to harness their potential to produce plants with novel traits. One important objective is the improvement of plant productivity to meet future demands in food crop production. Gene function is mostly characterized through overexpression or silencing in transgenic plants. This approach is a lengthy procedure, especially in cereals. Plant viral expression systems can be used for rapid expression of proteins. However, current systems have a small cargo capacity and have mostly been used for gene silencing. Here, a four-component Barley Stripe Mosaic Virus-based (BSMV) system with high cargo capacity was constructed for rapid and stable expression of recombinant proteins in different plant species allowing function analyses at different stages of development. Fluorescent marker proteins are expressed at high levels within a week and a proof of efficient function analysis is shown using the aluminum malate transporter-1 gene. In addition to the ability of gene cotransformation, this work demonstrates that the four-component BSMV system allows overexpression of cDNAs of up to 2100 nucleotides (encoding a protein of ca 78 kDa) thereby providing an invaluable tool to accelerate functional genomics and proteomic research in monocot and dicot species.