Trehalose accumulation contributes to Azospirillum argentinense Az19 stress endurance and improved water status of inoculated maize.

GARCÍA J.; PAGNUSSAT L.A.; CASANOVAS E.M.; GROPPA M.D.; CREUS C.; MARONICHE G.M.

Congreso; XVIII Congreso Argentino de Microbiología General ? SAMIGE 2022; 2022

Drought is one of the most concerning environmental threats in agriculture, both because of the damage that it causes on crops as well as for its increasing severity as a result of climate change. Azospirillum genus comprises plant-associated bacteria that produce multiple beneficial effects on their host, resulting in an increased root growth that enhance water and nutrient acquisition. Previously, we showed that A. argentinense Az19 has a high tolerance to osmotic stress in vitro, and is able to protect inoculated maize from the negative effects of drought. In this work, we tested the role of trehalose accumulation in stress endurance of A. argentinense Az19 and its plant-growth-promotion capacity. The recombinant strain A. argentinense Az19F, which carries a chromosomal copy of E. coli cytoplasmic trehalase gene treF under a constitutive promoter, was obtained using the miniTn7 system. As expected, the TreF-expressing mutant strain was unable to accumulate trehalose. Phenotypic characterization showed that A. argentinense Az19F produces lower auxin levels than the wild type strain, and is more sensitive to salt, osmotic and UV stress. Inoculation assays were then carried out to test the performance of strain Az19F, in comparison to A. argentinense Az19, to promote the growth of maize plants subjected to drought. Maize seeds were inoculated with strain Az19, Az19F or not inoculated, sown in pots and raised in a growth chamber. Non-stressed (control) or stressed groups were watered to 100% or 50% field capacity, respectively, before sowing. Plants of the control group were rewatered on demand for the rest of the assay. Fifteen days after sowing, plants were harvested and their growth (height, fresh and dry weight), water status, total antioxidant capacity and phenolic compounds levels, were analyzed. It was found that, in the absence of stress, inoculation with Az19 and Az19F improved maize growth similarly, with the exception of root dry weight which was not increased by the latter. Inoculation with Az19F also promoted the growth of stressed plants at the same extent than Az19, with exception of aerial dry weight which was lower in Az19F treatments. However, in contrast to Az19, Az19F was unable to improve the relative water content of maize plants under stress. Biochemical analysis of plants indicated that total antioxidant and phenolic compounds levels were unchanged by Az19 inoculation but were increased in Az19F-treated plants subjected to drought, suggesting that the mutant strain negatively affects maize oxidative status. In conclusion, it was established that trehalose production contributes to, but is not essential for, A. argentinense stress tolerance.