Pectin is
a plant cell wall polysaccharide made of mainly D-galacturonic acid (GA)
subunits. The potency of the filamentous fungus Aspergillus niger to naturally
secrete high amounts of pectinases to degrade pectin has been utilized for the
industrial production of pectinases. Industrially produced pectinases by A.
niger are subsequently used mainly in the food industry, and for the hydrolysis
of plant biomass to produce renewable energy. In this thesis, the key players
in the transcriptional regulatory system of pectinases in A. niger, such as the
transcriptional activator GaaR, the repressor GaaX and the physiological
inducer 2-keto-3-deoxy-L-galactonate, are discovered. Several approaches to
exploit this system for increased or constitutive expression of the genes
encoding pectinases are also presented, such as overexpression and constitutive
activation of gaaR, accumulation of 2-keto-3-deoxy-L-galactonate, and deletion
of gaaX or creA, the main transcriptional repressor involved in CCR.</p