Dodder (genus Cuscuta) is an example of a parasitic plant. That is, it derives some or all of its nutritional requirements from another living plant.
In a previous post, we saw how dodder seedlings may “sniff out” their victims.
A paper published in the journal Science (see Ref. 1 below) has provided evidence that “When dodder attacks a host plant, it opens up a conduit through which messenger [RNAs] and perhaps other regulatory RNAs are exchanged between parasite and host. Because a single dodder plant can attack multiple hosts, such exchanges may underlie instances of genes transferring between species.” (from Editor’s Summary Ref. 1 below).
This is not the first report of small bits of RNA acting as a potential means of communication within an organism and between different organisms.
“The ability of messenger RNAs (mRNAs) to move long distances in plants is well known. This mobility is thought to be controlled by the specific interactions between mRNAs and proteins that produce complexes capable of traversing plasmodesmatal pores into the phloem stream where they can be carried throughout the plant. Our understanding of this process has been limited by challenges in tracking specific mRNAs. In this issue of Nature Plants Thieme et al. [Ref. 2 below] describe a substantial step forward in characterizing mRNA mobility, revealing patterns of movement that suggest a broad scope and sophisticated regulation.” (from Ref. 3 below)
Of course, the main question about all of this is that, if small bits of RNA serve as a “language” among plants (and also among plants and fungi), then what are these organisms actually saying to each other?
There is some evidence that pathogenic fungi may use small bits of RNA to compromise the immune system of host plants (see for example small things considered).
It’s not unreasonable to expect that parasitic plants such as dodder use RNA trafficking to their advantage. For example, “…it is interesting to speculate whether RNAs from the parasite could be used as pathogenic factors in establishing and maintaining host connections.” (from Ref. 4 below).
Perhaps the greatest implication of all of this mobile RNA has to do with horizontal gene transfer.
As noted by the authors of Ref. 1 below:
“This widespread exchange of mRNA raises the possibility of horizontal gene transfer (HGT). Given what appears to be a constant exchange of mRNA between Cuscuta and its hosts, the relative prevalence of cases of HGT involving Cuscuta is not surprising. Although most documented cases of HGT in parasitic plants suggest a mechanism involving direct transfer of DNA, at least one case of HGT into a parasitic plant (Striga hermonthica) exhibits evidence of an RNA intermediate in the mechanism.“
1. Kim, G., et al. (2014) “Genomic-scale exchange of mRNA between a parasitic plant and its hosts.” Science, Vol. 345, pp. 808-811. (Abstract).
2. Thieme, C. J. , et al. (2015) “Endogenous Arabidopsis messenger RNAs transported to distant tissues.” Nature Plants, Article number: 15025 (Abstract).
3. Westwood, J. H. (2015) “RNA transport: Delivering the message.” Nature Plants, Article number: 15038.
4. LeBlanc, M., G. Kim and J. H. Westwood (2012) “RNA trafficking in parasitic plant systems.” Frontiers in Plant Science, Vol. 3, p. 203. (Full Text).
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