2019, DOI: 10.1038/s41477-019-0467-z
Field-grown tobacco plants maintain robust growth while accumulating large quantities of a bacterial cellulase in chloroplasts
Jennifer Schmidt, Justin McGrath, Maureen Hanson, Stephen Long, and Beth Ahner
High accumulation of heterologous proteins expressed from the plastid genome has sometimes been reported to result in compromised plant phenotypes. Comparisons of transplastomic plants to wild-type are typically made in environmentally-controlled chambers with relatively low light; little is known about the performance of such plants in field conditions. Here we report on two plastid-engineered tobacco lines expressing the bacterial cellulase Cel6A. Field-grown plants producing Cel6A at ~20% of total soluble protein (TSP) exhibit no loss in biomass or Rubisco content and only minor reductions in photosynthesis compared to wild-type. These experiments demonstrate that when grown in the field, tobacco possesses sufficient metabolic flexibility to accommodate high levels of the recombinant protein by increasing total protein synthesis and accumulation and/or by reallocating unneeded endogenous proteins. Based on current tobacco cultivation practices and readily achievable recombinant protein yields, we estimate that particular proteins could be obtained from field-grown transgenic tobacco plants at costs three orders of magnitude less than current cell culture methods.