AUTHOR=Su Fan , Jacquard Cédric , Villaume Sandra , Michel Jean , Rabenoelina Fanja , Clément Christophe , Barka Essaid A. , Dhondt-Cordelier Sandrine , Vaillant-Gaveau Nathalie 

TITLE=Burkholderia phytofirmans PsJN reduces impact of freezing temperatures on photosynthesis in Arabidopsis thaliana

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00810

DOI=10.3389/fpls.2015.00810

ISSN=1664-462X

ABSTRACT=<p>Several plant growth-promoting rhizobacteria (PGPR) are known to improve plant tolerance to multiple stresses, including low temperatures. However, mechanisms underlying this protection are still poorly understood. The aim of this study was to evaluate the role of the endophytic PGPR, <italic>Burkholderia phytofirmans</italic> strain <italic>PsJN</italic> (<italic>Bp PsJN</italic>), on <italic>Arabidopsis thaliana</italic> cold tolerance using photosynthesis parameters as physiological markers. Under standard conditions, our results indicated that <italic>Bp PsJN</italic> inoculation led to growth promotion of <italic>Arabidopsis</italic> plants without significant modification on photosynthesis parameters and chloroplast organization. However, bacterial colonization induced a cell wall strengthening in the mesophyll. Impact of inoculation modes (either on seeds or by soil irrigation) and their effects overnight at 0, -1, or -3°C, were investigated by following photosystem II (PSII) activity and gas exchanges. Following low temperatures stress, a decrease of photosynthesis parameters was observed. In addition, during three consecutive nights or days at -1°C, PSII activity was monitored. Pigment contents, RuBisCO protein abundance, expression of several genes including <italic>RbcS, RbcL, CBF1, CBF2, CBF3, ICE1, COR15a</italic>, and <italic>COR78</italic> were evaluated at the end of exposure. To assess the impact of the bacteria on cell ultrastructure under low temperatures, microscopic observations were achieved. Results indicated that freezing treatment induced significant changes in PSII activity as early as the first cold day, whereas the same impact on PSII activity was observed only during the third cold night. The significant effects conferred by <italic>PsJN</italic> were differential accumulation of pigments, and reduced expression of <italic>RbcL</italic> and <italic>COR78</italic>. Microscopical observations showed an alteration/disorganization in <italic>A. thaliana</italic> leaf mesophyll cells independently of the freezing treatments. The presence of bacteria during the three successive nights or days did not significantly improved <italic>A. thaliana</italic> responses but prevented the plasmalemma disruption under freezing stress.</p>