Cytokinins mediated resistance, biocontrol and biofertilization

Biological fertilizers based on microalgae have proven to be a successful alternative in the agricultural sector to reduce unnecessary chemicals that can have unwanted side effects. Previous studies have shown that microalgae have multiple effects on plants, such as inducing faster germination, promoting leaf and root growth, and increasing disease resistance. This study investigated the biocontrol and biological fertilizer abilities of natural highly CK-producer Chlamydomonas reinhardtii (Chl). A newly developed CRISPR/Cas9 Chl mutants (CK-deficit) were used to investigate the function of cytokinins (CKs) in Chl-mediated bacterial-induced resistance and plant seed germination and drought tolerance. In wild type CC125, there are 6156,6 pmol/g total CKs (including 30.2% CKs bases and 69.8% CKs nucleotides), 55.5% iP- type, 44.3% cZ-type, 0.2% tZ type were found by LC-MS. The CKs level of the isopentenyl transferase (IPT) mutants and the Lonely Guy Gene (LOG) mutants are 11,7 pmol/g and 1688,2 pmol/g, respectively. The biocontrol results showed the promotion of Nicotiana tabacum cultivar SR1 (NT) resistance to the Pseudomonas syringae pv. Tabaci (PstT) after infiltration with the wild-type strains of Chl. On the other hand, mutant strains deficient in the production and signaling of CKs showed a reduction in resistance promotion. Nevertheless, mutants indicated positive stimulation effects on drought tolerance in Arabidopsis. These results prove that CKs are an essential part of microalgae's ability to promote resistance to pathogens. Meanwhile, moderate CKs producing mutant Chl strains are good candidates as biofertilizers to improve the drought resistance in plants.