Callose deposition at plasmodesmata is a critical factor in restricting the cell-to-cell movement of Soybean mosaic virus

Abstract

Callose is a β-l,3-glucan with diverse roles in the viral pathogenesis of plants. It is widely believed that the deposition of callose and hypersensitive reaction (HR) are critical defence responses of host plants against viral infection. However, the sequence of these two events and their resistance mechanisms are unclear. By exploiting a point inoculation approach combined with aniline blue staining, immuno-electron microscopy and external sphincters staining with tannic acid, we systematically investigated the possible roles of callose deposition during viral infection in soybean. In the incompatible combination, callose deposition at the plasmodesmata (PD) was clearly visible at the sites of inoculation but viral RNA of coat protein (CP-RNA) was not detected by RT-PCR in the leaf above the inoculated one (the upper leaf). In the compatible combination, however, callose deposition at PD was not detected at the site of infection but the viral CP-RNA was detected by RT-PCR in the upper leaf. We also found that in the incompatible combination the fluorescence due to callose formation at the inoculation point disappeared following the injection of 2-deoxy-D-glucose (DDG, an inhibitor of callose synthesis). At same time, in the incompatible combination, necrosis was observed and the viral CP-RNA was detected by RT-PCR in the upper leaf and HR characteristics were evident at the inoculation sites. These results show that, during the defensive response of soybean to viral infection, callose deposition at PD is mainly responsible for restricting the movement of the virus between cells and it occurs prior to the HR response.

Small RNA Derived from the Virulence Modulating Region of the Potato spindle tuber viroid Silences callose synthase Genes of Tomato Plants

“…Callose deposition at the PD is a critical factor in restricting the cell-to-cell viral movement of Soybean mosaic virus (Li et al, 2012). Previous studies of the thermodynamic prediction of the PSTVd structure underscored the importance of some of its RNA motifs such as loops 7 and 8 of the VMR that are critical to both the viroid's replication and its systemic trafficking (Zhong et al, 2008).…”

“…21 dpi compared with 14 dpi can be attributed to the hypersensitive reaction of the plant's defense system against the invading pathogen (Li et al, 2012). To confirm the decreased expression of the CalS11-like mRNA, we performed RNA gel blot assays using probes specific to the CalS11-like mRNA and to PSTVd.…”

Study on Interactions between the Major Apple Valsa Canker Pathogen Valsa mali and Its Biocontrol Agent Saccharothrix yanglingensis Hhs.015 Using RT-qPCR

“…These changes may result from one or more of the following mechanism (s): 1) a direct effect of Hhs.015 inhibition on pathogen growth in the bark lesions, and/or 2) the indirect effect of a Hhs.015-stimulated increase in host resistance to the pathogen. A previous study has demonstrated that callose deposition in plasmodesmata was mainly responsible for restricting the movement of Soybean mosaic virus between plant cells contributing to the defensive response of soybeans to viral infection [14]. …”

“…Field trials showed that the recurrence rate of scraped lesions in V . mali - infected apple trees was stably controlled by Hhs.015 with a high level of efficiency (61.29%), which was comparable to common chemical agents such as difenoconazole and tebuconazole [14]. Early studies have shown that Hhs.015 produced heteroauxin, chitinase, proteinase and glucanase.…”

Cajal bodies and their role in plant stress and disease responses

“…97 For example, callose deposition may impose a direct physical barrier that restricts intercellular trafficking of the virus through the plasmodesmata. 105 Plant PARPs have also been implicated in differentiation and cell cycle control pathways, 97 which are known to overlap with components of plant signaling in response to stresses. Alterations in the poly(ADP-ribosyl)ation level induced by extrinsic (biotic or environmental) or intrinsic (genetic/physiological) cues play a central role in PARP-mediated cellular stress and developmental signaling processes; 96,97 however the detailed molecular mechanisms underlying the these processes remain largely uncharacterised.…”