Scientists find a new chemical to induce plant defences

Single-stranded DNA oligodeoxynucleotides (ssODNs) are molecules that are involved in the immune responses of mammals. A study by Laila Toum and colleagues published in Annals of Botany finds that ssODNs can induce protection against plant pathogens too. The team found ssODNs activated defence genes in Arabidopsis thaliana.

As nucleic acids are found in all kingdoms of life, it’s no surprise that organisms have tools for recognising them. These are either microbe-associated molecular patterns (MAMPs) or as damage-associated molecular patterns (DAMPs). There has been a lot of work on immunity in mammals, no doubt because humans are mammals. However, plant immunity is also activated by both DNA and RNA.

“While the immunostimulatory effect of single-stranded DNA (ssDNA) has been well characterized in mammals, it has not been investigated in plants,” write Toum and colleagues in their article. “In this work we found that ssODNs IMT504 and 2006, previously shown to activate immunity in mammalian cells, can protect A. thaliana from Botrytis cinerea and from Pst DC3000, but not from crucifer-infecting tobacco mosaic virus (TMV-Cg).”

Arabidopsis thaliana, rock cress, is a plant in the same family as brassicas like cabbages or turnips. It is very well studied as a model organism, which helps in recognising when something unusual is happening in the cells.

Induction of immunity in A. thaliana by IMT504 and 2006 has similarities with that elicited by other MAMPs, such as flagellin, since both ssODNs promoted stomatal closure, inhibited root elongation and induced the transcription of defence genes. The three responses were reduced in bak1-5 and bak1-5/bkk1 mutants, in which co-receptors involved in the perception of various elicitors of plant defence are affected.”

The authors state that while there are some similarities between ssODNs and other MAMPs, the signalling does not overlap completely. This means that the ssODNs could be using chemicals in a slightly different way to send infection signals around the plant.

“The use of synthetic oligonucleotides could shed light on the mechanism of stimulation of immunity by DNA, which might be a promising tool for crop protection and plant disease management,” conclude Toum and colleagues.