Rice tungro bacilliform virus: Difference between revisions

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Once the plant is infected, the symptoms induced by RTBV is stunting of the plant, red to yellow-orange discoloration, and the reduction of the amounts of grain harvested. Early infections will cause the death of the plant. [Kunii et al 2004] While the effect of the RTBV is significant on its own, its potential for damage increases when it is combined with RTSV. There has been some genetic resistance seen in plants against RTSV, but to date there is little, if any, genetic resistance being identified for RTBV.
Once the plant is infected, the symptoms induced by RTBV is stunting of the plant, red to yellow-orange discoloration, and the reduction of the amounts of grain harvested. Early infections will cause the death of the plant. [Kunii et al 2004] While the effect of the RTBV is significant on its own, its potential for damage increases when it is combined with RTSV. There has been some genetic resistance seen in plants against RTSV, but to date there is little, if any, genetic resistance being identified for RTBV.





Revision as of 16:54, 26 April 2009

Bacilliform virus particles of Rice tungro bacilliform virus (Courtesy H. Hibinovia www.apsnet.org)

Baltimore Classification

Higher order taxa

Viruses; Pararetro-transcribing viruses; Caulimoviridae; Tungrovirus;[NCBI link to find]

Species

Rice tungro bacilliform virus

NCBI: Taxonomy

Description and Significance

In 1975, RTBV was first recognized and then identified as a component member (along with Rice Tungro Spherical Virus (RTSV)) of the virus complex that is responsible for causing rice tungro disease. It is found to occur in Ortyza sativa and Ortyza sp. species of rice. [Saito et al 1975, Hibino et al 1978]



RTBV is transmitted from plant to plant exclusively by the green leafhopper, Nephotettix virescens. [Tyagi et al 2008] N. virescens can acquire RTBV in 30 minutes and can retain infectivity for up to 4 days. Nymphs transmit more efficiently than adults and females more efficiently than males. Transmission efficiency is also affected by temperature, increasing as the temperature rises from 10 to 34 degrees C. [Anjaneyulu et al 1995]

Green leafhopper and rice plants infected with RTBV(Courtesy Republic of the Phillipines - DOA)


Once the plant is infected, the symptoms induced by RTBV is stunting of the plant, red to yellow-orange discoloration, and the reduction of the amounts of grain harvested. Early infections will cause the death of the plant. [Kunii et al 2004] While the effect of the RTBV is significant on its own, its potential for damage increases when it is combined with RTSV. There has been some genetic resistance seen in plants against RTSV, but to date there is little, if any, genetic resistance being identified for RTBV.


The virus is associated with all rice growing countries of South and South-east Asia. The effect of the virus, while found in most cultivars, will vary in its intensity.

Rice tungro disease, the most important viral disease of rice, is widespread in South and Southeast Asia and is believed to be responsible for annual losses nearing 1 trillion US dollars worldwide (Herdt 1991).





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Genome Structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence?


(Courtesy of the Assoc.of Appl. Viruses) via http://www.dpvweb.net/notes/showmap.php?genus=Tungrovirus



Pararetroviruses have a DNA genome. The DNA of pararetroviruses accumulates within the nucleus as multiple copies of a circular, non-segmented chromosome molecule. The RTBV genome is a double stranded DNA of 8.0 kbp with two site-specific discontinuities resulting from replication by reverse transcriptase. The RTBV genome contains four open reading frames (ORF); the function of ORF 1,2, and 4 are unknown. ORF 3 is thought to be associated with cell-to-cell movement proteins, viral coat proteins, aspartate protease, and, most importantly, the replicase comprising reverse transcriptase and RNaseH activities. However, this has not been confirmed. [Hull 1996]

Virion Structure, Metabolism and Life Cycle

Interesting features of cell structure; how it gains energy; what important molecules it produces.


The RTBV virion consists of an unenveloped capsid in a bacilliform particle shape. It is approximately 30nm in diameter and has a length of 130 nm. The virion contains circular DNA in a single molecule and is a single coat protein species.

Tungrovirus virion 75%.jpg

Retroviruses have an RNA genome whereas pararetroviruses have a DNA genome; and, a proviral form of retroviruses is integrated into the host chromosome whereas the DNA of pararetroviruses accumulates within the nucleus as multiple copies of a circular chromosome The life cycle of RTBV is not well known but since its DNA structure does not intergrate into the host's DNA, RTBV's life cycle should follow the general viral reproduction life cycle: the viruses attach to the host cell, injects their contents into the cell nucleus, then change the host cell's metabolism to reproduce new viruses (molecular-biology.suite101.com/article.cfm/viruses). Like other viruses, everything resources have to come from the host.

Rice tungro bacilliform virus (RTBV) replicates only in phloem cells in infected rice plants and its promoter drives strong phloem-specific reporter gene expression in transgenic rice plants.

Ecology and Pathogenesis

Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

The habitat for RTBV is confined to rice cultivars, specifically Oryza sativa and Oryza sp. RTBV is restricted to vascular tissue and is found in sieve tubes of the plants.

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.



Yanhai Yin2, Qun Zhu3, Shunhong Dai1, Chris Lamb3 and Roger N. Beachy1 "RF2a, a bZIP transcriptional activator of the phloem-specific rice tungro bacilliform virus promoter, functions in vascular development "

Himani Tyagi Æ Shanmugam Rajasubramaniam Æ Manchikatla Venkat Rajam Æ.Indranil Dasgupta RNA-interference in rice against Rice tungro bacilliform virus results in its decreased accumulation in inoculated rice plants

Author

Page authored by Trung Lam and Mark Lebednick, students of Prof. Jay Lennon at Michigan State University. A Viral Biorealm page on the family Rice tungro bacilliform virus