Title:Characterization of the Chloroplast Genome Facilitated the Transformation of <i>Parachlorella kessleri</i>-I, A Potential Marine Alga for Biofuel Production
VOLUME: 21 ISSUE: 8
Author(s):Prachi Nawkarkar*, Sagrika Chugh, Surbhi Sharma, Mukesh Jain, Sachin Kajla and Shashi Kumar*
Affiliation:International Centre for Genetic Engineering and Biotechnology, New Delhi 110067, International Centre for Genetic Engineering and Biotechnology, New Delhi 110067, International Centre for Genetic Engineering and Biotechnology, New Delhi 110067, School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi 110067, Tata Steel Limited, Research & Development, P O Burmamines, Jamshedpur 831007, International Centre for Genetic Engineering and Biotechnology, New Delhi 110067
Keywords:Chloroplast genome, genetic engineering, homologous recombination, photosynthetic organism, microalgae biofuels,
parachlorella.
Abstract:
Introduction: The microalga Parachlorella kessleri-I produces high biomass and lipid content
that could be suitable for producing economically viable biofuel at a commercial scale. Sequencing
the complete chloroplast genome is crucial for the construction of a species-specific chloroplast
transformation vector.
Methods: In this study, the complete chloroplast genome sequence (cpDNA) of P. kessleri-I was assembled;
annotated and genetic transformation of the chloroplast was optimized. For the chloroplast
transformation, we have tested two antibiotic resistance makers, aminoglycoside adenine transferase
(aadA) gene and Sh-ble gene conferring resistance to spectinomycin and zeocin, respectively.
Transgene integration and homoplasty determination were confirmed using PCR, Southern blot and
Droplet Digital PCR.
Results: The chloroplast genome (109,642 bp) exhibited a quadripartite structure with two reverse repeat
regions (IRA and IRB), a long single copy (LSC), and a small single copy (SSC) region. The genome
encodes 116 genes, with 80 protein-coding genes, 32 tRNAs and 4 rRNAs. The cpDNA provided
essential information like codons, UTRs and flank sequences for homologous recombination to
make a species-specific vector that facilitated the transformation of P. kessleri-I chloroplast. The
transgenic algal colonies were retrieved on a TAP medium containing 400 mg. L-1 spectinomycin, but
no transgenic was recovered on the zeocin-supplemented medium. PCR and Southern blot analysis ascertained
the transgene integration into the chloroplast genome, via homologous recombination. The
chloroplast genome copy number in wildtype and transgenic P. kessleri-I was determined using Droplet
Digital PCR.
Conclusion: The optimization of stable chloroplast transformation in marine alga P. kessleri-I should
open a gateway for directly engineering the strain for carbon concentration mechanisms to fix more
CO2, improving the photosynthetic efficiency and reducing the overall biofuels production cost.
