INDUCTION OF HSP70 AND POLYUBIQUITIN EXPRESSION ASSOCIATED WITH PLANT-VIRUS REPLICATION

By examining the front of virus invasion in immature pea embryos infec ted with pea seed-borne mosaic virus (PSbMV), the selective control of different host genes has been observed, From our observations, the ea rly responses to PSbMV replication can be grouped into three classes, inhibited host gene expression, induced host gene expression, and no e ffect on a normal host function, The expression of two heat-inducible genes encoding HSP70 and polyubiquitin was induced coordinately with t he onset of virus replication and the down-regulation of two other gen es encoding lipoxygenase and heat shock cognate protein, The down-regu lation was part of a general suppression of host gene expression that mag be achieved through the degradation of host transcripts, We discus s the possibilities of whether the induction of HSP70 and polyubiquiti n genes represents a requirement for the respective protein products b y the virus or Is merely a consequence of the depletion of other host transcripts, The former is feasible, as the induction of both genes do es result in increased HSP70 and ubiquitin accumulation, This also ind icates that, in contrast to some animal virus infections, there is not a general inhibition of translation of host mRNAs following PSbMV inf ection, This selective control of host gene expression was observed in all cell types of the embryo and identifies mechanisms of cellular di sruption that could act as triggers for symptom expression.