## 1 Introduction  
Straw is an important source of roughage for herbivorous livestock. However, the degree of utilization is very low due to a lack of suitable and adequate methods. Most straw is discarded and burned on the spot, resulting in a waste of resources and generation of environmental pollution. Lignin, as a recalcitrant high molecular weight polymer, widely exists in straw tissue [1; 2; 3; 4]. Therefore, extensive research efforts are being undertaken to effectively degrade lignin and improve the utilization rate of straw forage. At present, microbial and enzymatic treatments are considered to be the best method for lignin degradation because of their low cost, low pollution and simple operation [5; 6]. White-rot fungi are the microorganisms with the highest potential for such microbial and enzymatic treatments because of their ability to completely degrade lignin to CO\({}_{2}\) and H\({}_{2}\)O [7; 8; 9]. _Phanerodontia chrysosporium_ is a white-rot fungus which secretes a family of lignin-degrading enzymes that are involved in the biodegradation of lignin and several environmental pollutants [10; 11]. In 1983, [PERSON] and [PERSON] reported that _P. chrysosporium_ secretes Lignin peroxidase (LiP) and Mn-dependent peroxidase (MnP) under nutrient limitation. They also studied the mechanism involved in biosynthesis of both enzymes and their role in lignin degradation. It was proposed that LiP and MnP play key roles in lignin degradation [12; 13]. This capability of _P. chrysosporium_ to produce lignin peroxididases and manganese peroxididases makes it a model organism for studying lignin-degrading enzyme systems. _P. chrysosporium_ has previously been proposed as an efficient biological resource for the production of LiP [14]. LiP, an oxidoreductaseate, is a monomer heme protein (molecular weight 38-43 kDa) secreted by _P. chrysosporium_[15]. It is the main lignin degradation enzyme in the process of lignin biodegradation [16; 17]. It can enzymatically hydrolyze lignin in straw, forage and feed seed coat, and as a result, improve the quality of feed materials, and, thus, improve the nutritional value [18]. Nonetheless, the LiP produced by wild-type strains isolated from the environment has shown some disadvantages, such as difficulty to use, proneness to inactivation, high nutritional requirements, low yield and low enzyme activity, which to a great extent hinder the large-scale application of LiP. Nevertheless, in recent years, to overcome these disadvantages, more and more lignin peroxidase genes (_lip_) from different sources have been cloned and expressed in heterologous hosts [19; 20; 21]. Therefore, it is important to study the expression of LiP. _Cyberlindnera jadini_ (former _Candida utilis_) is certified as a food-grade yeast by the Food and Drug Administration of the USA (FDA) and is used in the food, feed and pharmaceutical industries [22]. Extensive studies on _C. jadini_ have led to the development of a mature _C. jadini_ expression system. In selecting resistance markers, investigators have proposed the _L41_ gene present in the _C. jadini_ genome, which encodes the _L41_ ribosomal protein responsible for the cyclohesimide (CYH)-resistant phenotype in yeasts. Studies have shown that a CYH resistance gene can be obtained through mutating a single base in codon 56 of the _L41_ gene. This has provided a convenient method for the construction of a _C. jadini_ integrated expression vector [23]. GAP-p (glyceraldehyde-3-phosphate dehydrogenase promoter) is a strong constitutive promoter, which was successfully cloned from _C. jadini_[24]. The 18S rDNA sequence in _C. jadini_ is a highly repetitive unit and an effective strategy to increase the copy number of foreign genes in the yeast genome [25] in the absence of a stable plasmid in _C. jadini_. The integration of foreign genes into chromosomes using an integrated vector is the main approach for _C. jadini_ to introduce foreign genes into chromosomes [26; 27]. These findings confirm that _C.