Regulation of the reserve carbohydrate metabolism by alkaline pH and calcium in Neurospora crassa reveals a possible cross-regulation of both signaling pathways

Abstract

BackgroundGlycogen and trehalose are storage carbohydrates and their levels in microorganisms vary according to environmental conditions. In Neurospora crassa, alkaline pH stress highly influences glycogen levels, and in Saccharomyces cerevisiae, the response to pH stress also involves the calcineurin signaling pathway mediated by the Crz1 transcription factor. Recently, in yeast, pH stress response genes were identified as targets of Crz1 including genes involved in glycogen and trehalose metabolism. In this work, we present evidence that in N. crassa the glycogen and trehalose metabolism is modulated by alkaline pH and calcium stresses. ResultsWe demonstrated that the pH signaling pathway in N. crassa controls the accumulation of the reserve carbohydrates glycogen and trehalose via the PAC-3 transcription factor, which is the central regulator of the signaling pathway. The protein binds to the promoters of most of the genes encoding enzymes of glycogen and trehalose metabolism and regulates their expression. We also demonstrated that the reserve carbohydrate levels and gene expression are both modulated under calcium stress and that the response to calcium stress may involve the concerted action of PAC-3. Calcium activates growth of the Δpac-3 strain and influences its glycogen and trehalose accumulation. In addition, calcium stress differently regulates glycogen and trehalose metabolism in the mutant strain compared to the wild-type strain. While glycogen levels are decreased in both strains, the trehalose levels are significantly increased in the wild-type strain and not affected by calcium in the mutant strain when compared to mycelium not exposed to calcium.ConclusionsWe previously reported the role of PAC-3 as a transcription factor involved in glycogen metabolism regulation by controlling the expression of the gsn gene, which encodes an enzyme of glycogen synthesis. In this work, we extended the investigation by studying in greater detail the effects of pH on the metabolism of the reserve carbohydrate glycogen and trehalose. We also demonstrated that calcium stress affects the reserve carbohydrate levels and the response to calcium stress may require PAC-3. Considering that the reserve carbohydrate metabolism may be subjected to different signaling pathways control, our data contribute to the understanding of the N. crassa responses under pH and calcium stresses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3832-1) contains supplementary material, which is available to authorized users.

CRZ1 regulator and calcium cooperatively modulate holocellulases gene expression in Trichoderma reesei QM6a

“…Nutritional requirements and pH stress conditions control are targets of research among a wide number of fungal species, such as Neurospora crassa (Virgilio et al, 2017), Trichoderma harzianum (Moreno-Mateos and Codo, 2007) and T. reesei (He et al, 2014). However, the influence of several stress conditions, such as the effect of ion concentration exposure n transcription, still remain poorly understood in the industrial workhorse T. reesei.…”

Functional diversity in the pH signaling pathway: an overview of the pathway regulation in Neurospora crassa

“…However, little is known on how the reserve carbohydrates are regulated in microorganisms, mainly regarding which transcription factors are directly involved in this regulation under different environmental conditions. Both carbohydrate levels are highly dependent on pH in N. crassa; higher glycogen levels were observed under acidic pH (4.2), and lower glycogen and trehalose levels under alkaline pH (7.8) when compared to normal pH (5.8) (Cupertino et al 2012;Virgilio et al 2017). The PAC-3 transcription factor regulates the expression of most of the genes encoding enzymes involved in the metabolism of both carbohydrates and binds to their promoters under normal and alkaline pH (Cupertino et al 2012;Virgilio et al 2017).…”

“…Both carbohydrate levels are highly dependent on pH in N. crassa; higher glycogen levels were observed under acidic pH (4.2), and lower glycogen and trehalose levels under alkaline pH (7.8) when compared to normal pH (5.8) (Cupertino et al 2012;Virgilio et al 2017). The PAC-3 transcription factor regulates the expression of most of the genes encoding enzymes involved in the metabolism of both carbohydrates and binds to their promoters under normal and alkaline pH (Cupertino et al 2012;Virgilio et al 2017). All the PAL components, with the exception of PAL-9 (the PalI/Rim9 ortholog), were required for the proper levels of glycogen and trehalose under normal and alkaline pH (Virgilio et al 2017), suggesting the requirement of an active pH signaling pathway.…”

Calcineurin responsive zinc‐finger‐1 binds to a unique promoter sequence to upregulate neuronal calcium sensor‐1, whose interaction with MID‐1 increases tolerance to calcium stress in Neurospora crassa

“…The well‐studied target of calcineurin in fungi is the calcineurin‐responsive zinc finger 1 (Crz1) that translocates into the nucleus when dephosphorylated by the activated calcineurin, and regulates target gene expression (Chen et al , ). The N. crassa Crz1 homologue, encoded by the crz‐1 gene (NCU07952) contains two DNA binding C 2 H 2 Zinc‐finger domains (Virgilio et al , ). In S. cerevisiae , the knockout mutant of the CRZ‐1 shows similar, but less severe phenotypes compared to calcineurin mutants, while overexpression of the CRZ1 rescues calcineurin mutant phenotypes (Stathopoulos and Cyert, ).…”