Production of leafy biomass using temporary immersion bioreactors: an alternative platform to express proteins in transplastomic plants with drastic phenotypes

Chloroplast transformation technology is a promising approach for the production of foreign proteins in plants with expression levels of up to 70 % of total soluble protein (TSP) achieved in tobacco. However, expression of foreign protein in the chloroplast can lead to drastic or even lethal effects in transplastomic plants grown in soil, thereby potentially limiting the applicability of this technology. For instance, previous attempts to express the outer surface protein A (OspA) from Borrelia burgdorferi in tobacco chloroplasts led to plant death when expressed at 10 % TSP. We show here that this earlier transplastomic line, as well as a new plant line, OspA:YFP, expressing OspA fused to the yellow fluorescent protein, can be propagated in temporary immersion bioreactors (TIBs) using AlkaBurst™ technology to produce leafy biomass that expressed OspA at levels of up to 7.6 % TSP, to give a maximum yield of OspA of about 108 mg/L. Our results show that TIBs provide an alternative method for the production of transplastomic biomass expressing proteins toxic for plants and is a particularly useful approach when ‘absolute’ containment is required.