In most organisms, tiny bits of RNA play key roles in genetic expression. They do this by docking to appropriate genic sequences in just the right places to affect expression. This craft is practiced both within and among cells.
This modulation mechanism is called RNA interference (RNAi). “RNAi can travel,” says Swiss geneticist Olivier Voinnet.
RNAi messaging is especially helpful in plants, which have immovable cells but a need to communicate among plant parts to coordinate growth and defense – flexibility in development called “phenotypic plasticity.”
RNAi is targeted. Rather than wasteful, full-plant broadcasts, RNA messages are sent by certain cells to other specific cells or regions. Proteins keep an eye out for siRNA (small interfering RNA) missives addressed to them.
The number of such watchful proteins (called AGOs) varies depending upon a plant part’s condition. “The amount and diversity of AGO proteins in traversed cells coupled to the siRNA-intrinsic signatures function together as a kind of molecular sieve, the form of which may differ from cell type to cell type along the siRNA path. Depending on the spatial configuration of this sieve, a wide variety of siRNA movement patterns can be produced. AGOs can be induced by stress or developmental signals such that the spatial shape of the sieve can change and evolve at any time,” reports Voinnet.
This RNA messaging is a peephole into a coherent, comprehensive system of plant intelligence, even as plants lack any identifiable physical organs for their savvy.
“The amazing travels of small RNAs,” ScienceDaily (28 July 2020).
Emanuel A. Devers et al, “Movement and differential consumption of short interfering RNA duplexes underlie mobile RNA interference,” Nature Plants (6 July 2020).