A thermophilic endophytic fungus Thielavia subthermophila Q22 enhances straw biodegradation, plant thermotolerance, and pathogen resistance for sustainable agriculture

Endophytic fungi are pivotal for sustainable agriculture due to their roles in lignocellulosic waste conversion, plant stress resilience, and pathogen control. Here, we characterize Thielavia subthermophila Q22, a thermophilic endophyte isolated from Platycladus orientalis. Q22 demonstrated exceptional thermostability with optimal growth at 45 °C and hydrolyzed corn straw at 39% efficiency, which was attributed to its high endoglucanase activity (752 U/mL). The strain enhanced crop productivity, increasing bok choy germination by 116.4%, soybean height by 28.5%, and bok choy biomass by 36.8%. Furthermore, the Q22 achieved an inhibition rate of 54% against the pathogen Sclerotinia sclerotiorum, which was associated with its high chitinase activity (500 U/mL at 45 °C). Additionally, Q22 upregulated the expression of plant heat shock proteins (HSPs) and their transcription factors (HSFs) (2- 25-fold), boosting thermotolerance. This work establishes Q22 as a circular bioeconomy tool that integrates agricultural waste valorization, crop resilience, and biocontrol, reducing reliance on chemical inputs.