MAPK CcSakA of the HOG Pathway Is Involved in Stipe Elongation during Fruiting Body Development in Coprinopsis cinerea

Abstract

Mitogen-activated protein kinase (MAPK) pathways, such as the high-osmolarity glycerol mitogen-activated protein kinase (HOG) pathway, are evolutionarily conserved signaling modules responsible for transmitting environmental stress signals in eukaryotic organisms. Here, we identified the MAPK homologue in the HOG pathway of Coprinopsis cinerea, which was named CcSakA. Furthermore, during the development of the fruiting body, CcSakA was phosphorylated in the fast elongating apical part of the stipe, which meant that CcSakA was activated in the apical elongating stipe region of the fruiting body. The knockdown of CcSakA resulted in a shorter stipe of the fruiting body compared to the control strain, and the expression of phosphomimicking mutant CcSakA led to a longer stipe of the fruiting body compared to the control strain. The chitinase CcChiE1, which plays a key role during stipe elongation, was downregulated in the CcSakA knockdown strains and upregulated in the CcSakA phosphomimicking mutant strains. The results indicated that CcSakA participated in the elongation of stipes in the fruiting body development of C. cinerea by regulating the expression of CcChiE1. Analysis of the H2O2 concentration in different parts of the stipe showed that the oxidative stress in the elongating part of the stipe was higher than those in the non-elongating part. The results indicated that CcSakA of the HOG pathway may be activated by oxidative stress. Our results demonstrated that the HOG pathway transmits stress signals and regulates the expression of CcChiE1 during fruiting body development in C. cinerea.

Effects of β-1,6-Glucan Synthase Gene (FfGS6) Overexpression on Stress Response and Fruit Body Development in Flammulina filiformis

“…We proposed that the expression of FfGS6 may be necessary for cell wall synthesis during the stipe elongation of F. filiformis ; however, a single elevation in cellular FfGS6 expression may lead to the excessive accumulation of β-1,6-glucan, thereby inhibiting the stipe elongation of F. filiformis . Since stipe elongation is one of the most complex biological process of fungi and could be regulated by multiple genes [ 42 , 43 ]. Needless to say, more studies are needed to verify this speculation.…”

Transcriptome Profiling Reveals Candidate Genes Related to Stipe Gradient Elongation of Flammulina filiformis

“…Niu et al suggested that the stipe cell wall architecture varies in elongation and non-elongation regions, and the thickness of stipe cell wall is inversely proportional to the cell elongation rate [ 8 ]. It was also demonstrated that several proteins and signaling pathways could mediate stipe cell extension and are involved in stipe elongation [ 5 , 6 , 10 , 13 , 14 ]. However, the stipe is usually treated as an entire organization in most transcriptome studies [ 42 , 43 ], and the transcriptional landscape of stipe gradient elongation remains to be clarified.…”

“…Several studies suggested that glucanase, chitinase, and β-glucan-degrading enzymes associated with cell wall extension are involved in stipe elongation regulation [ 9 , 10 , 11 , 12 ]. In addition, the genes encoding septin protein Cc.Cdc3 and MAPK homologue CcSakA were also suggested to have important roles in controlling stipe elongation in C. cinerea [ 13 , 14 ]. In F. filiformis , the fruiting body at a length of 8.5 cm was defined as the elongation stage; in this stage, the apical 1.5 cm showed a fast elongation rate, the 1.5–3 cm section showed a slow elongate rate, and the region below 3 cm showed no further elongation [ 6 ].…”