The mitogen-activated protein kinase GlSlt2 regulates fungal growth, fruiting body development, cell wall integrity, oxidative stress and ganoderic acid biosynthesis in Ganoderma lucidum.

The mitogen-activated protein kinases (MAPKs) are crucial signaling instruments in eukaryotes that play key roles in regulating fungal growth, development, and secondary metabolism and in adapting to the environment. In this study, we characterized an Slt2-type MAPK in Ganoderma lucidum, GlSlt2, which was transcriptionally induced during the primordium and fruiting body stages. RNA interference was used to examine the function of GlSlt2. Knockdown of GlSlt2 caused defects in growth and increased hyphal branching as well as hypersensitivity to cell wall-disturbing substances. Consistently, the chitin and ß-1,3-d-glucan contents and the expression of cell wall biosynthesis genes were decreased and down-regulated, respectively, in GlSlt2 knockdown strains compared with those in the wild type (WT). In addition, no primordium or fruiting body could be observed in GlSlt2 knockdown strains. Furthermore, the intracellular reactive oxygen species (ROS) content and ganoderic acid biosynthesis also decreased in GlSlt2 knockdown strains. Addition of H2O2 could recover the decreased ganoderic acid content in GlSlt2 knockdown strains, indicating that GlSlt2 might regulate ganoderic acid biosynthesis via the intracellular ROS level. Overall, GlSlt2 is involved in hyphal growth, fruiting body development, cell wall integrity, oxidative stress and ganoderic acid biosynthesis in G. lucidum.

Transcript and metabolite alterations increase ganoderic acid content in Ganoderma lucidum using acetic acid as an inducer.

Acetic acid at 5-8 mM increased ganoderic acid (GA) accumulation in Ganoderma lucidum. After optimization by the response surface methodology, the GA content reached 5.5/100 mg dry weight, an increase of 105% compared with the control. The intermediate metabolites of GA biosynthesis, lanosterol and squalene also increased to 47 and 15.8 µg/g dry weight, respectively, in response to acetic acid. Acetic acid significantly induced transcription levels of sqs, lano, hmgs and cyp51 in the GA biosynthesis pathway. An acetic acid-unregulated acetyl coenzyme A synthase (acs) gene was selected from ten candidate homologous acs genes. The results indicate that acetic acid alters the expression of genes related to acetic acid assimilation and increases GA biosynthesis and the metabolic levels of lanosterol, squalene and GA-a, thereby resulting in GA accumulation.

Functions of the nicotinamide adenine dinucleotide phosphate oxidase family in Ganoderma lucidum: an essential role in ganoderic acid biosynthesis regulation, hyphal branching, fruiting body development, and oxidative-stress resistance.

Ganoderma lucidum has drawn worldwide interest with regard to its secondary metabolism and pharmaceutical activity. However, the development of such research has been limited because of a lack of basic biological knowledge. Nicotinamide adenine dinucleotide phosphate oxidases (Nox) have recently been highlighted because of the many important biological roles in plants and animals; however, the exact functions of Nox are still not fully understood in fungi. In this study, we identified two Nox isoforms (NoxA and NoxB) and a regulator, NoxR. RNA interference was used, and silencing of the Nox isoforms and NoxR expression indicated a central role for these genes in hyphal branching, fruiting body development, reactive oxygen species (ROS) generation, ROS resistance and ganoderic acid biosynthesis regulation. Further mechanistic investigation revealed that Nox-generated ROS elevated cytosolic Ca(2+) levels by activating a plasma membrane Ca(2+) influx pathway, thereby inducing the Ca(2+) signal pathway to regulate ganoderic acid biosynthesis and hyphal branching. Importantly, our results highlight the Nox functions in signal crosstalk between ROS and Ca(2+), and these findings provide an excellent opportunity to identify the potential pathway linking ROS networks to calcium signalling in fungi and suggest that plants, animals and fungi share a conserved signal-crosstalk mechanism.