Molecular characteristics and pathogenicity of infectious cDNA clones of the Chinese isolates of pea enation mosaic virus 1 and pea enation mosaic virus 2

Abstract

The pea enation mosaic disease (PEMD) causes significant yield losses worldwide. PEMD is caused by two taxonomically unrelated but symbiotic viruses, pea enation mosaic virus 1 (PEMV-1) and pea enation mosaic virus 2 (PEMV-2). In this study, the complete genomes of four isolates of PEMV-1 and PEMV-2 from Yunnan Province of China were determined and analyzed. The four isolates of PEMV-1 or PEMV-2 shared ≥ 98.7% nucleotide sequence identities at whole genome level. The four Chinese PEMV-1 isolates were most closely related to PEMV-1-Ramsey-1 with nucleotide sequence identities of 97.8–98.0%, while the four Chinese PEMV-2 isolates were most closely related to PEMV-2-DSMZ PV-0088, with nucleotide sequence identities of 94.3–94.5%. The two full-length infectious cDNA clones of the Yunnan-Dali isolates of the two viruses (PEMV-1-YDL and PEMV-2-YDL) were constructed. Co-inoculation of PEMV-1-YDL and PEMV-2-YDL in pea seedlings caused systemic infection, with typical enation and mosaic symptoms on new leaves after inoculation, while the inoculated Nicotiana benthamiana plants showed curling symptoms. Inoculation of pea seedlings with either PEMV-1-YDL or PEMV-2-YDL did not cause obvious symptoms on the new leaves. It has been known that PEMV-2 helps the systemic infection of PEMV-1. However, our results showed that PEMV-1-YDL alone could cause a systemic infection. The pathogenicity of the two infectious clones was tested on different pea cultivars, and some cultivars were PEMD-tolerant. This is the first report of the infectious clones constructed from the Chinese isolates of PEMV-1 and PEMV-2. The current approach will facilitate determination of the synergistic relationship between PEMV-1 and PEMV-2 and their interactions with the host plant by reverse genetic analysis.