DECREASED SUSCEPTIBILITY TO VIRAL DISEASE OF BETA-1,3-GLUCANASE-DEFICIENT PLANTS GENERATED BY ANTISENSE TRANSFORMATION

Antifungal class I beta-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection, Unexpectedly, mutants deficient in these enzymes generated by antisens e transformation showed markedly reduced lesion size, lesion number, a nd virus yield in the local-lesion response of Havana 425 tobacco to t obacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necro sis virus, These mutants also showed decreased severity of mosaic dise ase symptoms, delayed spread of symptoms, and reduced yield of virus i n the susceptible response of N. sylvestris to TMV, The symptoms of di sease in the responses of both plant species were positively correlate d with beta-1,3-glucanase content in a series of independent transform ants. Taken together, these results provide direct evidence that beta- 1,3-glucanases function in viral pathogenesis, Callose, a substrate fo r beta-1,3-glucanase, acts as a physical barrier to the spread of viru s, Callose deposition in and surrounding TMV-induced lesions was incre ased in the beta-1,3-glucanase-deficient, local-lesion Havana 425 host , suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to inf ection, Our results suggest novel means, based on antisense transforma tion with host genes, for protecting plants against viral infection, T hese observations also raise the intriguing possibility that viruses c an use a defense response of the host against fungal infection-product ion of beta-1,3-glucanases-to promote their own replication and spread .