Characterization and expression of XPH1 , the hydrophobin gene of the lichen‐forming ascomycete Xanthoria parietina

• Molecular genetics of wall surface hydrophobicity of the lichen-forming ascomycete Xanthoria parietina was explored. In a previous study XPH11, a class 1 hydrophobin, was isolated from the symbiotic phenotype collected in nature. • A genomic library of aposymbiotically cultured Xanthoria parietina was constructed and screened for the hydrophobin gene XPH1. Gene expression was explored with in situ hybridization techniques. • The encoded protein contained 110 amino acids, including a secretion signal; the open reading frame was interrupted by two introns. XPH1 was differentially expressed in the symbiotic phenotype, high expression being evident in medullary hyphae of the vegetative thallus and of the thalline margin of apothecia; these are in contact with the algal layer and prevent the thalline interior from becoming waterlogged, a prerequisite for gas exchange of the photobiont. No signal was detected in either the hydrophilic cortex, the conidiomata, the hymenial and subhymenial layers of apothecia, or in the aposymbiotically cultured mycobiont. The data for Northern blot analyses correlated with those of in situ hybridization studies. • XPH1 may fulfil important roles for the functioning of the symbiotic relationship.