38The yeast-like fungus Aureobasidium pullulans PL5 is a microbial antagonist against postharvest 39 pathogens of fruits. The strain is able to produce hydrolases, including glucanases, chitinases and 40 proteases. The alkaline serine protease gene ALP5 from A. pullulans was cloned, inserted into the 41 vector pPIC9 to construct pPIC9/PL5, and then expressed in Pichia pastoris strain KM71. ALP5 42 had a molecular mass of 42.9 kDa after 5 days growth with 1% methanol induction at 28 °C. The storage technologies are available (Khamis et al., 2012; Martini et al., 2013; Snowdon, 1990). To
78Among the different biocontrol agents, yeasts are promising and gaining popularity (Jamalizadeh et 79 al., 2011; Janisiewicz et al., 2010; Spadaro et al., 2008). In particular, the yeast-like fungus
80Aureobasidium pullulans De Bary (Arnaud), showed to be effective against B. cinerea, P.
81expansum and Rhizopus stolonifer on various fruit, including apple, grapes, sweet cherry, 82 strawberry and peach (Bencheqroun et al., 2007; Ippolito et al., 2000; Lima et al., 1997; Schena et 83 al., 2003). Moreover, the strain PL5 of A. pullulans showed high efficacy in the control of B.84 cinerea and P. expansum on apples, in addition to Monilinia laxa on plums and peaches (Zhang et 85 al., 2010a).
86Several mechanisms have been reported to play a significant role in the biocontrol activity of A.
87pullulans strains, including induction of defence responses (Ippolito et al., 2000) and competition
88for nutrients (Bencheqroun et al., 2007). Recently, it was demonstrated that the strain PL5 secretes protease (Zhang et al., 2010a; 2012).
91In mycoparasitism, fungal proteases may be significantly involved in antagonistic activity, because 92 they may play a significant role in fungal cell wall lysis, which is composed of chitin and glucan 93 polymers embedded in, and covalently linked to a protein matrix (Wessels, 1986
Construction of the expression vector pPIC9-ALP5
156The product was subsequently digested with EcoRI and ligated into the pPIC9 vector, which was The pPIC9-ALP5 construct was linearized by Stu I enzyme for efficient integration into the P.
165pastoris genome, then it was transformed into P. pastoris strain KM71. were done to confirm whether the protease cDNA was integrated into the genomic DNA of P.
171pastoris. Primers used for PCR, 5'AOX1 (5'-GACTGGTTCCAATTGACAGC-3') and 3'AOX1
172(5'-GCAAATGGCATTCTGACATCC-3') were provided by the manufacturer. DC and DP refers to the average diameters of fungal mycelia of control and protease respectively.
227The experiment was performed three times.
Results
271
Expression and purification of recombinant protease
272The expression of purified recombinant protease from a transformed isolate of P. pastoris was 273 analysed through SDS-PAGE (Figure 1). After 120 h induction, the protease band was observed in 274 some isolates at 42.9 kDa, which corresponds to the same molecular weight of the ALP5 protease selected for large-scale expression. The recombinant protein was e...