The coat protein of Alternanthera mosaic virus is the elicitor of a temperature-sensitive systemic necrosis in Nicotiana benthamiana, and interacts with a host boron transporter protein

•Alternanthera mosaic virus CP is an elicitor of systemic necrosis in N. benthamiana.•Virus-induced systemic necrosis is enhanced at 15 °C compared to 25 °C.•Induction of systemic necrosis is dependent on as few as two CP amino acid residues.•These residues are at subunit interfaces within the same turn of the virion helix.•Inducer/non-inducer CPs interact differentially with a boron transporter protein.

Different isolates of Alternanthera mosaic virus (AltMV; Potexvirus), including four infectious clones derived from AltMV-SP, induce distinct systemic symptoms in Nicotiana benthamiana. Virus accumulation was enhanced at 15 °C compared to 25 °C; severe clone AltMV 3-7 induced systemic necrosis (SN) and plant death at 15 °C. No interaction with potexvirus resistance gene Rx was detected, although SN was ablated by silencing of SGT1, as for other cases of potexvirus-induced necrosis. Substitution of AltMV 3-7 coat protein (CPSP) with that from AltMV-Po (CPPo) eliminated SN at 15 °C, and ameliorated symptoms in Alternanthera dentata and soybean. Substitution of only two residues from CPPo [either MN(13,14)ID or LA(76,77)IS] efficiently ablated SN in N. benthamiana. CPSP but not CPPo interacted with Arabidopsis boron transporter protein AtBOR1 by yeast two-hybrid assay; N. benthamiana homolog NbBOR1 interacted more strongly with CPSP than CPPo in bimolecular fluorescence complementation, and may affect recognition of CP as an elicitor of SN.