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The lichen-forming fungus was isolated from the desert lichen Endocarpon pusillumthat is extremely drought resistant. To understand the molecular mechanisms of drought resistance in the fungus, we employed RNA-seq and quantitative real-time PCR to compare and characterize the differentially expressed genes in pure culture at two different water levels and with that in desiccated lichen. The comparative transcriptome analysis indicated that a total of 1781 genes were differentially expressed between samples cultured under normal and PEG-induced drought stress conditions. Similar to those in drought resistance plants and non-lichenized fungi, the common drought-resistant mechanisms were differentially expressed in E. pusillum. However, the expression change of genes involved in osmotic regulation in E. pusillumis different, which might be the evidence for the feature of drought adaptation. Interestingly, different from other organisms, some genes involved in drought adaption mechanisms showed significantly different expression patterns between the presence and absence of drought stress in E. pusillum. The expression of 23 candidate stress responsive genes was further confirmed by quantitative real-time PCR using dehydrated E. pusillumlichen thalli. This study provides a valuable resource for future research on lichen-forming fungi and shall facilitate future functional studies of the specific genes related to drought resistance.

This study investigated the photosynthetic rate of the lichen Endocarpon pusillumat the Chinese Academy of Sciences Shapotou Desert Research Station and estimated its annual contribution to the carbon budget in the ecosystem. The software SigmaPlot 10.0 with “Macro-Area below curves” was used to calculate the carbon fixation capacity of the lichen. The total carbon budget (ΣC) of the lichen was obtained by subtracting the respiratory carbon loss (ΣDR) from the photosynthetic carbon gain (ΣNP). Because water from precipitation plays an important role in photosynthesis in this ecosystem, the annual carbon budget of E. pusillumat the station was estimated based on the three-year average precipitation data from 2009 to 2011. Our results indicate that the lichen fixes 14.6 g C m−2annually. The results suggest that artificial inoculation of the crust lichen in the Tengger Desert could not only help reduce the sand and dust storms but also offer a significant carbon sink, fixing a total of 438000 t of carbon over the 30000 km2of the Tengger Desert. The carbon sink could potentially help mitigate the atmospheric greenhouse effect. Our study suggests that the carpet-like lichen E. pusillumis an excellent candidate for “Bio-carpet Engineering” of arid and semi-arid regions.