Programmed responses to virus replication in plants.

Abstract Despite their economic importance, we understand very little about the mechanism leading to symptom formation in compatible virus infections. By applying a spatial analysis to advancing infection fronts, we have been able to relate molecular events in small groups of cells to a sequence of virus-induced changes. This sequence starts ahead of the main front of virus replication and virus protein accumulation and lasts beyond the time at which virus replication has ceased. The host changes include alterations in gene expression, physiology and cellular ultrastructure. The relationship between these effects has been analysed in comparative studies between different virus infections in different hosts and abiotic stress. The research points to there being common features for different viruses leading to common effects. Also, although many of the consequences of virus infection are similar to the effects of heat shock, there are sufficient differences to suggest that the two inducers use distinct control pathways. The immediate challenge for the future is to establish synchronous infections of tissues so that the complex relationship between the virus and the host can be investigated using temporal rather than spatial analyses.