During the same period, it is important to emphasize that the daily increase in mycelial mass remained constant. A positive correlation between cp gene expression and chlamydospores formation was found (Fig. 4). The transcript level increased from the conidium status to the second day of growth, where hyphae were present and chlamydospores just began to be formed. The highest increase occurred at day 3 (Log2 fold change = 6.15), which preceded the maximum increase in chlamydospores concentration observed

at the fourth day post-inoculation. Conidia used to inoculate the plates were known GSI-IX to have a low level of cp transcript (Bernardi et al., 2011) and were used as calibrator (time zero). The analysis of a 1368 bp region upstream of the ATG codon for the presence of putative regulatory motifs revealed a putative TATA box at position −167 and putative CCAAT boxes at positions −634 and −817 (Fig. 5). Moreover, putative motifs involved in the regulation of gene expression in response to stress and developmental cues were identified. Two CATTCY sites bound by transcription factor of the TEA/ATTS family, such as yeast Tec1p (Köhler et al., 2002) and Aspergillus nidulans AbaA, were located at positions −297 and −1258. In A. nidulans, the abaA gene controls the expression of the genes

involved in morphogenesis and developmental regulation and is required in the final stages of conidiophore development and in spore maturation (Andrianopoulos & Timberlake, 1994). Three stress response elements (STRE) were found at positions

−293, −415 and −782 (Marchler GSK126 mw et al., 1993) together with a putative binding site Glycogen branching enzyme for the Nrg1/Nrg2 Zn finger repressors at position −400. In yeast, these two regulatory sequences are associated with the promoters of many genes that respond to a variety of stress conditions (Vyas et al., 2005). Finally, two recognition sites for the yeast Skn7 regulators involved in the response to stress such as oxidative stress and high osmolarity stress were found at positions −713 and −963 (Morgan et al., 1997; Izumitsu et al., 2007). The present work showed for the first time a significant correlation between regulation of the cp gene and growth of C. platani: when fungal growth was reduced, the cp gene expression was down-regulated; when the growth level was increased, it was instead up regulated. In addition, the expression of the cp gene appeared to be positively correlated with the differentiation process of chlamydospores. The modulation of transcription had already been analysed in some studies concerning cp and other cerato-platanins, but without taking into account the growth level of the fungus and not so extensively as in the present work (Wilson et al., 2002; Chagué et al., 2006; Djonović et al., 2006; Seidl et al.