Physiological and transcriptional analysis of the effects of aluminum stress on Cryptococcus humicola

Aluminum (Al) toxicity is a major factor that limits crop productivity in acid soils. The toxic effects of Al exposure on Al-tolerant Cryptococcus humicola were analyzed at the physiological level. The exposure to 20 mM Al led to a clear increase in malondialdehyde content and a significant decrease in the levels of protein carbonyls, suggesting that Al stress caused oxidative damage to membrane lipids but not to proteins. Suppression subtractive hybridization (SSH) results showed that when C. humicola was exposed to 20 mM Al, a total of 141 ESTs were differentially expressed. Of them, 27 had unknown functions and 48 were newly identified in this study. The genes with known functions were categorized into seven groups. The largest group was related to metabolism and energy, followed by protein synthesis and processing, cell structure, signal transduction and transcription, transporters, stress and defense. Reverse transcription (RT)-PCR analysis of certain genes was performed to confirm the reliability of the SSH data. Nine selected genes were upregulated by Al in a time-dependent manner. The potential functions of some genes involved in Al-tolerance were predicted and are discussed. The diversity of the putative functions of these genes indicates that Al stress results in a complex response in C. humicola .