Decreased Susceptibility to Viral Disease of b-1,3-Glucanase-Deficient Plants Generated by Antisense Transformation

Abstract

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 antisense transformation showed markedly reduced lesion size, lesion number, and virus yield in the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus in the susceptible response of N. sylvestris to TMV. The symptoms of disease in the responses of both plant species were positively correlated with [beta]-1,3-glucanase content in a series of independent transformants. Taken together, these results provide direct evidence that [beta]-1,3-glucanases function in viral pathogenesis. Callose, a substrate for [beta]-1,3-glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased 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 infection. Our results suggest novel means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection[mdash]production of [beta]-1,3-glucanases[mdash]to promote their own replication and spread.

Induction of systemic resistance against tobacco mosaic virus by Ningnanmycin in tobacco

“…Many studies have confirmed that the b-1,3-glucanases play a role in mechanism involved in resistance to pathogenic infection, which are coordinately induced in response to pathogenic infection and it can be considered as pathogenesis-related protein of tobacco [28][29][30][31][32]. Our results demonstrated that that the activity of b-1,3-glucanases obviously increased in the presence of NNM (Fig.…”

Resistance gene-dependent plant defense responses.

“…The constitutive plasma membrane-localized callose synthase enzyme catalyses the formation of this, P-1,3-glucan polymer and requires both increased levels of the primer P-furfuryl-P-glucoside and Ca2+ for activity (Kauss, 1990;Ohana et al, 1993). Blockage of plasmodesmata with callose is an essential component of the defense response required to impede cell-to-cell movement of viruses (Beffa et al, 1996).…”

Altered expression of an ankyrin-repeat protein results in leaf abnormalities, necrotic lesions, and the elaboration of a systemic signal

“…Some components of this response, such as the antifungal class I b-1, 3-glucanases (GLU I) and chitinases (CHN I), which are vacuolar PR-related proteins, act in concert to defend against a specific class of pathogens, fungi. Studies of deficient mutants suggest that GLU I may have dual defense-and counter defense-functions (Beffa et al, 1996;Iglesias and Meins, 2000a, b). Local induction of GLU I in response to virus infection actually increases the susceptibility of the plant to virus and appears to act, at least in part, by degrading callose at the cell surface important for reducing plasmodesmatal transport and virus spread (Bucher et al, 2001).…”