Alexey writes:

Dear TWiV hosts,

I am writing to you for the first time, although I have been listening for 5 or 6 years. I used to work as a virology/molecular biology lab researcher, studying, in different years, plant viruses, HIV and miRNAs. Several years ago, I quit lab research to do private teaching/tutoring, and am enjoying it so far. However, I keep myself up-to-date with literature in several fields of interest. Your TWiX podcasts are invaluable source of information for me.

The nanovirus paper by Sicard et al (TWiV-539) is so interesting, and the problem of replication of multicomponent/multipartite viruses is very fascinating.

Small terminological comment: Symplasmic pathway means transport through plasmodesmata – unique and fascinating specialized channels, connecting the cytoplasm of neighbouring plant cells: (here is one of recent reviews: Apoplasmic pathway corresponds to transport through intercellular space, along cell walls of plant cells.

Nanovirus is a phloem-limited (phloem-restricted) virus, so it can be found only (or predominantly) in three cell types that form phloem: sieve elements, companion cells, and phloem parenchyma. I don’t think that all eight particles have to be present in the same individual insect vector. They can be delivered, in different combinations, by several individual insects, as each plant in nature would be expected to be attacked by more than one individual insect. In any case, all eight segments have to be delivered into the same plant. And they are delivered by aphids to essentially the same cell, because aphids take sap from the sieve elements of the phloem, which are fused together (and connected through enlarged plasmodesmata of the sieve plate) into one functional unit – sieve tube. However, sieve elements lack nuclei, ribosomes and some other organelles, and while being live cells, entirely depend on companion cells for the supply of metabolites. Obviously, nanovirus cannot replicate in sieve elements. To replicate, viral ssDNA has to be delivered from sieve elements through plasmodesmata to companion cells or phloem parenchyma cells. And it is this delivery that should represent a bottleneck (or one of them) for nanovirus. Indeed, if a DNA segment  of only one type is present per cell, the cells would need to exchange viral mRNAs or viral proteins essential for replication, for example, M-Rep (initiator of replication), movement protein, cell cycle resetting protein, and nuclear shuttle protein. Also, transport of genomic ssDNA and coat protein to the site of assembly needs to occur. All these exchange events between cells where replication/transcription/translation of separate DNA components occur, are possible through plasmodesmata, considering the fact that many viral movement proteins are able to modify plasmodesmata, increasing their size exclusion limit. Moreover, plasmodesmata between companion cells and sieve elements already have increased size exclusion limit by default (compared, for example, to plasmodesmata between mesophyll cells), so if the nanovirus assembly occurs in sieve elements, DNA and coat protein would be able to move there. However, because of my ignorance, I do not know where exactly assembly of nanoviruses occurs. Yet, I would like authors to show not only transport of M-Rep protein between cells, but also transport of all other viral proteins. And I entirely agree with Vincent that the formation of infectious virions needs to be formally shown here. This may also require the precise site of assembly to be established and detected first. Otherwise, very interesting paper. I used to work with plant viruses that have only three components, but here we have eight, so conceptually this is certainly a much more difficult problem to tackle – for both nanovirus and researchers 🙂

Please keep up your excellent work on science communication! I absolutely admire your work on virology education, from plant viruses to vaccination of humans to many other topics.

It’s +4 Celcius (-5 with wind chill) and light rain in Toronto – good weather to stay inside and listen to TWiV 🙂

Best regards,


Alexey Karetnikov, Ph.D.

CEO, Research Consultant and Tutor

Alexey Karetnikov Tutoring: Science for Success


Anthony writes:

Lady with a cannon?

I guess Dr. Condit already got in touch, but in Austin there was a woman who stopped the moving of state records by firing a cannon.  If memory serves me correctly, she meant to hit the people working for Sam Houston, but missed. The sound of the cannon fire served as an alarm and the records — and state capitol — remained in Austin.  Did something similar really happen in Iowa? In Austin, there is a statue outside of the State House commemorating the event.

Justin writes: nts-attack-us-science-panel

David writes:

Dear Twivstars,

I was just listening to twiv 537 (yet another great episode!) and had to laugh about Dickson’s “bat on a stick” bush meat propaganda.  I wrote in because I actually once came by a street vendor selling fried bats – in Battambang, Cambodia, and a very pleasant city to stroll in or visit.  I must admit that even for local Khmer people who do not shy away from fried tarantulas or ant soup (not to mention fermented fish) this was a step too far and the vendor did not seem to have a thriving business.  However, hunger can do a lot to people.

Another thing is the ongoing massacre of the name Leeuwenhoek. Originally from Belgium (Flemish/Dutch speaking part) I only later came to  realize that Dutch has much more sounds than any other European languages, and tricky ones for that.  Kudos for Dickson who came pretty close (although everyone doubted whether that was how it was supposed to a dinner while he was visiting.  In any case, it should not be a Germanised version like “Löwenhuck” that was uttered by some of the otherwise very noble and esteemed professors.  While I am not entirely convinced by the google translate pronunciation, it may serve as a general guideline

Sorry for the pedantry, but I thought you might want to solve the riddle.

Best regards from a hot and windy Jinotepe, Nicaragua,

David Dionys

Anthony writes:

Anti-Vaxxers Have Said Pretty Dumb Things Throughout The Year, But These 15 Are Off The Charts

One is: If vaccines are so great, why aren’t they mentioned in the Bible?


How many people does it take to write a No. 1 hit? In the case of Travis Scott’s smash “Sicko Mode,” which came out Aug. 3, 2018, and has been on Billboard’s Hot 100 chart every week since, 30 different songwriters are credited.

# # #

In science papers with similarly top heavy pedigree, most contributions are also a dab of this and a pinch of that?  How many papers are produced really by teams like the building of a house, a film production or an orchestra performance?  Is there training for someone to be project manager or conductor for science papers?


I’d not known about this.  I’ve not been near an airport for nearly ten years.  Perhaps these cameras are common there.

Connor writes:

Dear TWIV team,

I have been listening to you all for about four years now – since my second year of undergrad. You all have been with me through community college, my first PCRs, to now, as I listen while writing my M.S. thesis. I am getting in touch because I find myself at a crossroads and I am not sure which way to turn.

I have been in a great, very productive, unique research lab for the past three years working on a topic I find incredibly interesting. The core focus of the lab is not my discipline (it’s an engineering lab, while I’m a biochemist), but they’ve let me design my own interdisciplinary projects to get at really novel, exciting science. I was originally planning on applying for PhD programs now in the next year. But the lab I’ve been in just asked me to stay with them for a PhD. I would have opportunities to apply for funding for projects based on experiments I designed, and I would be set to graduate in 3-4 years. The science is really exciting and hard to walk away from.

But I don’t know if I should stay. Setting aside that staying at the same lab for undergrad and graduate school is generally looked down upon, I have only worked on one topic for the past four years – when there’s a world of science out there. I listen to these podcasts and every week I hear something new that I find really exciting. Then again, I also read horror stories of ill-tempered PIs and toxic work environments. I know my current lab is nothing like that.

I guess the bottom line is – do I stick with what I know – a great research environment, great science, and great opportunities, or do I continue to explore the science that’s out there?  

I apologize for meandering and the butchering of commas. It’s just thesis fever. All advice is appreciated – I respect your collective opinions very much.

Best wishes from Virginia,