Cytokinin-deficient CRISPR/Cas9 mutants of Chlamydomonas reinhardtii
show reduced ability to prime resistance of tobacco against bacterial
infection
Abstract
Microalgae play an essential role in agriculture as bio-fertilizers and
biostimulants, but some also produce various plant hormones, such as
cytokinins (CK). CK are a class of natural plant hormones and there is
evidence that exogenous or bacterial CK can modulate plant defense.
However, there is a lack of knowledge about the effect of specific
microalgae or microalgae-produced cytokinins on this response. In our
study, we have evaluated the cytokinins-producing microalgae
Chlamydomonas reinhardtii (Cri) on its ability to prime
Nicotiana tabacum plant defenses against its natural pathogen
Pseudomonas syringae pv. tabaci. Our work functionally
verifies that Cri primes plant defense response, with cytokinins
being a crucial component. We have used the CRISPR/Cas9 system to
generate Cri LOG and IPT gene knockouts, which are
major points of the CK biosynthesis pathways. While Cri shows
strong protection potential, the CK-deficient mutants have a reduced
ability to affect plant defense, where the degree of protection
correlates with the CK levels - the IPT mutants show less
protection than the LOG mutants. Additionally, by measuring plant
defense gene expression by RTq-PCR we have shown that Cri
treatment stimulates tobacco defense response by priming.