Deletion of the KU70 homologue facilitates gene targeting in Lipomyces starkeyi strain NRRL Y-11558

Abstract

The objective of this study was to disrupt the non-homologous end-joining (NHEJ) pathway gene (Lsku70Δ) and evaluate the effects of selected gene deletions related to glycogen synthesis (LsGSY1) and lipid degradation (LsMFE1, LsPEX10, and LsTGL4) on lipid production in the oleaginous yeast Lipomyces starkeyi. Disruption of the NHEJ pathway to reduce the rate of non-homologous recombination is a common approach used to overcome low-efficiency targeted deletion or insertion in various organisms. Here, the homologue of the LsKU70 gene was identified and disrupted in L. starkeyi NRRL Y-11558. The LsGSY1, LsMFE1, LsPEX10, LsTGL4, and LsURA3 genes were then replaced with a resistance marker in the Lsku70Δ strain and several site-specific insertions were assessed for targeted over-expression of selected genes. The targeted disruption efficiency of five selected genes (LsGSY1, LsMFE1, LsPEX10, LsTGL4, and LsURA3) was increased from 0 to 10% in the parent to 50-100% of transformants screened in the Lsku70Δ strain with 0.8-1.4 kb homologous flanking sequences, while the efficiency of site-specific gene insertion with the β-glucuronidase reporter gene was 100% in the locus near the 3'-end coding (LsKU70) and non-coding (LsGSY1, LsMFE1, and LsPEX10) regions. Disruption of LsKU70 in isolation and in conjunction with LsGSY1, LsMFE1, LsPEX10, or LsTGL4 did not affect lipid production in L. starkeyi. Furthermore, β-glucuronidase reporter gene activity was similar in strains containing site-specific targeted insertions. Therefore, over-expression of genes related to lipid synthesis at targeted loci can be further examined for improvement of total lipid production in L. starkeyi.

Keywords: Homologous recombination; Lipid production and degradation; Lipomyces starkeyi; LsKU70; Non-homologous end-joining (NHEJ); Oleaginous yeast.