Overexpression of nicotinamide mononucleotide adenylyltransferase (nmnat) increases the growth rate, Ca2+concentration and cellulase production inGanoderma lucidum

Identifying new and economical means to utilize diverse lignocellulosic biomass is an urgent task.Ganoderma lucidumis a well-known edible and medicinal basidiomycete with an excellent ability to degrade a wide range of cellulosic biomass, and its nutrient use efficiency is closely related to the activity of extracellular cellulase. Intracellular nicotinamide adenine dinucleotide (NAD(+)) biosynthesis is controlled in response to nutritional status, and NAD(+)is an essential metabolite involved in diverse cellular processes. Nicotinamide mononucleotide adenylyltransferase (NMNAT) is a common enzyme in three NAD(+)synthesis pathways. In this study, a homologous gene ofnmnatwas cloned fromG. lucidumand twoG. lucidumoverexpression strains, OE::nmnat4 and OE::nmnat19, were constructed using anAgrobacterium tumefaciens-mediated transformation method. TheG. lucidum nmnatoverexpression strains showed obviously increased colony growth on different carbon sources, and intracellular Ca(2+)concentrations in theG. lucidumOE::nmnat4 and OE::nmnat19 strains were increased by 2.04- and 2.30-fold, respectively, compared with those in the wild-type (WT) strains. In theG. lucidumOE::nmnat4 and OE::nmnat19 strains, endo-beta-glucanase (CMCase) activity increased by approximately 2.8- and 3-fold, while beta-glucosidase (pNPGase) activity increased by approximately 1.9- and 2.1-fold, respectively, compared with the activity in the WT strains. Furthermore, overexpression of NAD(+)synthesis pathways was found to elicit cellulase production by increasing the intracellular Ca(2+)concentration. In summary, this study is the first to demonstrate that increased intracellular NAD(+)contents through overexpression of thenmnatgene of NAD(+)synthesis pathways may increase cellulase production by increasing intracellular Ca(2+)concentrations inG. lucidum.