Posts Tagged ‘Brazil’

Silence(d) is Golden (mosaic)…

12 October, 2011

Geminivirus particle: characteristic doubled icosahedron containing a single ssDNA (courtesy Russell Kightley)

About that title…I read in my Nature News on the iPad about the use of siRNA in transgenic beans to silence expression of the Bean golden mosaic begomovirus, and I irresistibly thought of this…B-)

To serious matters – said article reported the following:

“Brazilian scientists roll out a transgenic pinto bean (Phaseolus vulgaris) engineered to fend off one of the crop’s most devastating enemies: the golden mosaic virus. Approved on 15 September by the Brazilian National Technical Commission on Biosafety (CTNBio), the transgenic bean uses RNA interference to shut down replication of the virus [reported originally in Mol Plant Microbe Interac in 2007].”

This paper reported the following:

“…we explored the concept of using an RNA interference construct to silence the sequence region of the AC1 viral gene and generate highly resistant transgenic common bean plants. Eighteen transgenic common bean lines were obtained with an intron-hairpin construction to induce post-transcriptional gene silencing against the AC1 gene. One line (named 5.1) presented high resistance (approximately 93% of the plants were free of symptoms) upon inoculation at high pressure (more than 300 viruliferous whiteflies per plant during the whole plant life cycle) and at a very early stage of plant development. “

OK, some background: Bean golden mosaic virus (BGMV) is a begomovirus, a representative of the largest genus of the Geminiviridae, and one of the more devastating viral plant pathogens on the planet.  It is a single-stranded circular DNA virus with a very distinct particle morphology, which replicates its genome by a rolling circle mechanism shared by all geminiviruses, nanoviruses, circoviruses, microviruses and pretty much any other ssDNA virus, as well as some plasmids.

RNA silencing – once known as post-transcriptional gene silencing, before the field was usurped by non-plant virologists – is a natural mechanism used by plants in particular as an adaptive immune response to plant viruses, as well as to control gene expression.  It is a complicated process, involving the formation of double-stranded RNAs from complementary sequences, transcribed from DNA or RNA genomes, which are then chopped up into shorter 21-25 base-length sequences.  These small interfering (si) RNAs are dissociated, and are free to bind to complementary sequences in the plant cell cytoplasm – and target them for degradation by a particular set of enzymes.  This happens frequently in transgenic plants, where the desired over-expression of a particular gene may be frustrated by the plant promptly silencing it.  It is also part of an arms race between plant viruses and plants, with nearly all plant viruses demonstrating some ability to interfere with siRNA silencing.

Geminiviruses are no exception: a number of papers have explored silencing suppression by geminiviruses, with a review by Dave Bisaro prominent among them.  Who is also famous for singing “Born to be Wild” in a Spanish karaoke bar in 1994 with a number of other geminivirologists, who called themselves “Subgroup IV” – but I digress.

It is interesting, then, that one can make transgenic plants expressing siRNA specific for a geminivirus gene – and get silencing of viral expression, and effective immunity to the virus: this would seem to have potential for a deathmatch, with the plant trying to silence virus-coded RNA, while the virus tries to suppress RNA silencing by the plant…as well as the fact that it is a DNA virus, and silencing is mediated at the level of cytoplasmic RNA.

But it obviously works – and probably because the siRNA is being expressed constitutively, meaning the virus infecting the first cell(s) gets shut down before it has a chance to get expression going.  The choice of gene – the “AC1” or Rep – is also important, as expression of mRNA from this is at a very low level, and it is crucial for virus genome replication.  This means that shutting it down stops any DNA replication from occurring.

So Viva! Brasil, Viva! as we South African are fond of saying.  Southern hemisphere rules geminivirus resistance, OK…because we have more than a passing interest in the same phenomenon…B-)

Deadly Export

4 December, 2008

Hot on the heels of the arenavirus outbreak in South Africa recently – traced back to Zambia – comes the story of an unfortunate South African business traveller who took sick and then died in Brazil recently.  While it has been in the papers, as always, ProMED does it best:


Date: Wed, 3 Dec 2008 13:34:00 -0500 (EST)

From: ProMED-mail <>

Subject: PRO/AH/EDR> Viral hemorrhagic fever – Brazil (02): (RJ) ex South Africa




A ProMED-mail post


ProMED-mail is a program of the

International Society for Infectious Diseases <>


Date: Tue 2 Dec 2008

Source: Ministry of Health, Brazil (in Portuguese trans. & summ.

Mod.MPP, edited]




[The following additional information has been added to the Brazilian Ministry of Health statement included in the preceding ProMED-mail

post: Viral hemorrhagic fever – Brazil (RIO) ex South Africa: RFI, archive number 20081202.3792]


1. A 53-year-old man arrived in Brazil on 23 Nov [2008]. On 25 Nov [2008] he presented the 1st symptoms of a febrile hemorrhagic disease as yet undiagnosed.


2. On [28 Nov 2008], he went to 2 private hospitals in Rio de Janeiro, with a clinical picture of fever, chills, vomiting, hematuria, hepatomegaly, and small skin eruptions [?petechiae]. On [2 Dec 2008], the patient died.


5. One of the viruses suspected to be the cause of death of the patient is an [South African] arenavirus. It can be transmitted by direct contact with secretions or blood from rodents or from infected patients.


– —

Communicated by:

Naomi Bryant

Senior Information Analyst

National Travel Health Network and Centre (NaTHNaC) United Kingdom <>


[Previously it was stated that there had been no reports of similar symptoms among health professionals who had contact with the patient, and that implementation of quarantine was not considered necessary.

Diagnoses of dengue, malaria, and ebola [hemorrhagic fever] had already been discarded. Other etiologies, such as leptospirosis, hepatitis, and hantaviruses will be investigated.


This additional new information suggests that the South African visitor had contracted his illness prior to arrival in Brazil, and not during travel within the country. The patient’s illness had been diagnosed as a viral hemorrhagic fever and the results of laboratory tests are awaited. There is as yet no direct evidence that the patient had contracted the novel arenavirus recently identified as the cause of an outbreak of disease associated with the treatment of a Zambian patient in South Africa. – Mod.CP]


Now it is a matter of fact that there are plenty of nasty arenaviruses and other haemorhhagic fever agents in South America: however, getting sick only two days after arrival would tend to point to an external (and probably South African) source for the infection.


Which, if it is an arenavirus, is rather worrying – given that we have seen such a thing only recently, and only in a very limited context.


I am sure the folk at the National Institute for Communicable Diseases (NICD) in Johannesburg, and especially the Special Pathogens Unit, who do surveillance for these sorts of nasties, are going to be busy – let us wish them luck.


 And latest news (9/12/08): The Mail & Guardian web site carries this story as of 8th December.

SA man in Brazil did not die from arenavirus, says NICD


The death of a South African man in Brazil was not caused by the arenavirus, the National Institute for Communicable Diseases (NICD) said on Monday.

The institute’s deputy director, Dr Lucille Blumberg, said laboratory tests had tested negative for the virus.

Tick-bite fever, acquired in South Africa, is the likely cause of the illness, as indicated by tests performed by the reference laboratory in Brazil.”

The fever, she said, was a well-documented cause of severe illness. It did not pose any risks to those who had been in close contact with infected people. — Sapa

And can be cured with antibiotics, seeing as it is caused by a rickettsial-type prokaryote.