Cardiolipin synthesis inPseudomonas fluorescensUM270 plays a relevant role in stimulating plant growth under salt stress

Abstract

AbstractMembrane cardiolipin (CL) phospholipids play a fundamental role in the adaptation of bacteria to various environmental conditions, including saline stress. Here, we constructed deletion mutants of two CL synthetase genes,clsAandclsB, in the rhizobacteriumPseudomonas fluorescensUM270, and evaluated their role in plant growth promotion under salt stress.P. fluorescensUM270 ΔclsAand ΔclsBmutants showed a significant reduction in CL synthesis compared to the UM270 wild-type strain (58% ΔclsAand 53% ΔclsB), and their growth rate was not affected, except when grown at 100 and 200 mM NaCl. Additionally, the root colonization capacity of both mutant strains was impaired compared with that of the wild type. Concomitant with the deletion ofclsAandclsB, some physiological changes were observed in the UM270 ΔclsAand ΔclsBmutants, such as a reduction in indole acetic acid and biofilm production. By contrast, an increase in siderophore biosynthesis was observed. Further, inoculation of the UM270 wild-type strain in tomato plants (Lycopersicon esculentumSaladette) grown under salt stress conditions (100 and 200 mM NaCl) resulted in an increase in root and shoot length, chlorophyll content, and dry weight. On the contrary, when each of the mutants(ΔclsAand ΔclsB) were inoculated in tomato plants, a reduction in root length was observed when grown at 200 mM NaCl, but the shoot length, chlorophyll content, and total plant dry weight parameters were significantly reduced under normal or saline conditions (100 and 200 mM NaCl), compared to UM270 wild-type-inoculated plants. In conclusion, these results suggest that CL synthesis inP. fluorescensUM270 plays an important role in the promotion of tomato plant growth under normal conditions, but to a greater extent, under salt-stress conditions.