Abstract:
Furoviruses possess divided positive-stranded RNA genome, separately encapsidated in rigid rod-shaped particles and transmitted by plasmodiophorid 'fungi' in soil. They have a wide host range and world wide distribution. Among ten furoviruses, SBWMV, OGSV, RSNV, SgCSV infect cereals, BNYVV, BSBV, PMTV infect root or tuber crops and BBNV, PCV and IPCV infect leguminous crops. This paper reviews the information on general characteristics, vector transmission and molecular pathology of furoviruses. However, transmission properties of other plant viruses with fungal vectors have also been summarized. The molecular based mechanism of virus transmission by fungal vector, for some better characterized furoviruses and role of readthrough protein and other genes in virus transmission process, have also been briefly discussed. The analysis of nucleotide sequences of SBWMV, BNYVV, PMTV, PCV and BSBV indicated heterogeneity among furoviruses and have at least three kinds of genome organization. However, read-through proteins (RT) are a common feature in furoviruses and are found in BNYVV, SBWMV, PMTV and BSBV. The BNYVV RT protein is involved in particle assembly and transmission of the virus by P. betae. Repeated manual transmission of BNYVV, SBWMV, PMTV results in spontaneous deletions of RT domain and lose the ability of transmission through vector. PMTV-S, a field isolate, was efficiently acquired and transmitted by a monofungal culture of S. subterranea whereas PMTV-T which has 543 nt deletion in the 3' half of the RT, could not be acquired and transmitted by the same fungus. The association of lack of transmissibility of PMTV-T with-in apparent deletion of sequence in RT, relative to RT of transmissible isolate PMTV-S suggests that the RT domain, encoded by PMTV-S RNA 3 contains determinants that play an important role in the acquisition and transmission of PMTV by S. subterranea.
The mechanism by which virus particles move into or out of protoplasm of zoospore, needs further investigation. However, the process by which aviruliferous zoospores acquire virus particles in vivo, has been proposed. Recent progress in molecular pathological strategies, to protect crop plants against furoviruses, has also been briefly discussed.