Enhanced UV Resistance and Improved Killing of Malaria Mosquitoes by Photolyase Transgenic Entomopathogenic Fungi

Abstract

The low survival of microbial pest control agents exposed to UV is the major environmental factor limiting their effectiveness. Using gene disruption we demonstrated that the insect pathogenic fungus Metarhizium robertsii uses photolyases to remove UV-induced cyclobutane pyrimidine dimers (CPD) and pyrimidine (6-4) photoproducts [(6-4)PPs] from its DNA. However, this photorepair is insufficient to fix CPD lesions and prevent the loss of viability caused by seven hours of solar radiation. Expression of a highly efficient archaeal (Halobacterium salinarum) CPD photolyase increased photorepair >30-fold in both M. robertsii and Beauveria bassiana. Consequently, transgenic strains were much more resistant to sunlight and retained virulence against the malaria vector Anopheles gambiae. In the field this will translate into much more efficient pest control over a longer time period. Conversely, our data shows that deleting native photolyase genes will strictly contain M. robertsii to areas protected from sunlight, alleviating safety concerns that transgenic hypervirulent Metarhizium spp will spread from mosquito traps or houses. The precision and malleability of the native and transgenic photolyases allows design of multiple pathogens with different strategies based on the environments in which they will be used.

Stress response signaling and virulence: insights from entomopathogenic fungi

“…Transgenic expression of a melanin biosynthetic pathway, tyrosinase, or a highly active photolyase derived from archaebacteria resulted in increased resistance to sunlight and Uv exposure (Fang and St Leger 2012;Shang et al 2012;Tseng et al 2011). expression of a bacterial thioredoxin in B. bassiana increased fungal resistance to oxidative, heat, and Uv-B irradiation .…”

The role of three calcineurin subunits and a related transcription factor (Crz1) in conidiation, multistress tolerance and virulence in Beauveria bassiana

“…Error bars, SD from three independent cDNA or protein samples catalases (CatB and CatP) are the main contributors to total SOD and catalase activity in B. bassiana Wang et al 2013a). Interestingly, these genes and two other genes essential for UV damage repair (Fang and St Leger 2012) were down-regulated to various degrees in our deletion mutants. In addition, intracellular mannitol and trehalose levels are crucial for fungal multistress tolerance (Elbein et al 2003;Liu et al 2009) and were also reduced in our deletion mutants; this appeared to be associated with altered transcription patterns of those genes responsible for the biosynthesis and hydrolysis of both of these low-molecular solutes.…”

Improving mycoinsecticides for insect biological control

“…Dopaminebased melanins (L-DOPA and L-3,4-dihydroxyphenylalanine) can be synthesized via the activity of membrane bound laccases or tyrosinases (Cu-containing monooxygenases), and transformation of B. bassiana with an Aspergillus fumigatus tyrosinase increased resistance to UV-exposure as well as virulence . Although entomopathogenic fungi contain photolyase enzymes for repair of UV-induced cyclobutane pyrimidine dimers, expression of a highly efficient archaeal photolyase from Halobacterium salinarum resulted in strains with 32-fold improvement in survivability to sunlight (Fang and St Leger 2012). Increasing the expression of endogenous proteins involved in stress response has also led to strain improvements.…”