Regulation of a phenylalanine ammonia lyase (BbPAL) by calmodulin in response to environmental changes in the entomopathogenic fungus Beauveria bassiana

Abstract

Phenylalanine ammonia lyase (PAL, E.C. 4.3.1.5) catalyses the deamination of (L)-phenylalanine to trans-cinnamic acid and ammonia, facilitating a critical step in the phenylpropanoid pathway that produces a variety of secondary metabolites. In this study, we isolated BbPAL gene in the entomopathogenic fungus Beauveria bassiana. According to multiple sequence alignment, homology modelling and in vitroPAL activity, we demonstrated that BbPAL acts as a typical PAL enzyme in B. bassiana. BbPAL interacted with calmodulin (CaM) in vitro and in vivo, indicating that BbPAL is a novel CaM-binding protein. The functional role of CaM in BbPAL action was to negatively regulate the BbPAL activity in B.bassiana. High-performance liquid chromatography analysis revealed that (L)-phenylalanine was reduced and trans-cinnamic acid was increased in response to the CaM inhibitor W-7. Dark conditions suppressed BbPAL activity in B.bassiana, compared with light. In addition, heat and cold stresses inhibited BbPAL activity in B.bassiana. Interestingly, these negative effects of BbPAL activity by dark, heat and cold conditions were recovered by W-7 treatment, suggesting that the inhibitory mechanism is mediated through stimulation of CaM activity. Therefore, this work suggests that BbPAL plays a role in the phenylpropanoid pathway mediated by environmental stimuli via the CaM signalling pathway.