Functional analysis of NSs and NSm genes of Impatiens necrotic spot virus found in Salinas valley, California
Y. KUO (1), S. T. Koike (2), R. L. Gilbertson (1)
(1) University of California, Davis, Davis, CA, U.S.A.; (2) University of California, Davis, Salinas, CA, U.S.A.
Phytopathology 101:S95

In the 2006–2007, lettuce plants in Monterey County California showed necrotic spotting and mottle/mosaic symptoms, which were subsequently shown to be caused by Impatiens necrotic spot virus (INSV). Sequence analysis of N and NSs genes confirmed that lettuce-infecting INSV isolates were similar to previously characterized INSV isolates, and RT-PCR was used to investigate the INSV inoculum source(s). INSV was detected in thrips (Frankliniella occidentalis) from infected and non-infected lettuce and some asymptomatic weeds, such as malva and shepherd’s purse. This indicates that weeds are an inoculum source. To investigate properties of INSV proteins, the NSs and NSm were expressed alone or as fusions with GFP for subcellular localization and silencing suppressor experiments. Both NSs and NSm were expressed in Nicotiana benthamiana plants via Agrobacterium tumefaciens-mediated transient expression. Confocal laser scanning microscopy results showed that NSm formed punctate bodies in the cell membrane or wall, whereas NSm localized at the nuclear periphery and cytoplasm. Silencing suppressor experiments in N. benthamiana 16c GFP transgenic plants, and RNA binding assays with NSs and NSm are ongoing. Based on our preliminary data and previous studies on other tospoviruses, NSs may be the silencing suppressor of INSV.