enhances freezing tolerance and post-thaw recovery in by stimulating the expression of genes.

The root endophytic fungus plays an important role in increasing abiotic stress tolerance of its host plants. To explore the impact of on freezing tolerance, seedlings were co-cultivated with exposed to -6°C for 6 h. Freezing stress decreased the survival rate, electrolyte leakage, leaf temperature, water potential and chlorophyll fluorescence of plants in comparison to the controls. colonizion reduced the negative effects of freezing, and the plants contained also higher amounts of soluble proteins, proline and ascorbic acid during the post-thaw recovery period (4°C; 12 h). In contrast, the HO and malondialdehyde levels were reduced in seedlings colonized by the fungus. The brassinolide (BR) and abscisic acid (ABA) levels dramatically increased and the transcript levels of several crucial freezing-stress related genes (s, s, and ) were higher in inoculated plants during the post-thaw recovery period. Finally, inocculated mutants impaired in the freezing tolerance response (such as for INDUCER OF CBF EXPRESSION1, a crucial basic helix-loop-helix transcription factor for the cold-response pathway in , -2, -3 for C-REPEAT-Binding Factor, and for COLD-REGULATED and encoding the SUMO E3 LIGASE) showed better survival rates and higher expression levels of freezing-related target genes after freezing compared to the inocculated controls. Our results demonstrate that confers freezing tolerance and better post-thaw recovery in , and stimulates the expression of several genes involved in the CBF-dependent pathway.