Towards a synthetic biology platform for the production of in vitro plant biomass

Abstract

To meet climatic targets, we require an urgent shift from the petroleum industry, alongside concerted rewilding efforts to sustain vital natural carbon sinks and biodiversity. Sourcing materials and fuels from plants is a sustainable alternative to fossil fuels. Herein, plant cell suspension cultures (PCCs) are an attractive production platform which retain the innate capabilities of plants without competing for arable land. To-date, their use is mainly confined to the production of high-value products such as medicines and additives. This thesis proposes to expand their useable range to the alternative production of plant primary biomass products, including highly cellulosic biomass for the creation of paper pulp or biofuels. The in vitro growth of these materials would obviate the need for natural resource extraction and could circumvent environmentally unfriendly processes involved in pulping.

Desired biomaterials usually rely on specific, differentiated cell types, such as tracheary elements (TEs). PCCs however generally consist of dedifferentiated or stem-cell like cells. The work presented in this thesis therefore sought to create tools and methods to differentiate PCCs, pursuing a main objective to achieve highly cellulosic, de-lignified xylogenic cultures for the creation of in vitro paper pulp.

To realise these goals, a suite of novel genetic parts and protocols for use in plant synthetic biology were developed and characterised. These were employed to create constructs housing heterologous transcription factors known to be involved in xylary differentiation, which were applied to drive cell fate determination in PCCs. In addition, this work investigated phytohormone guided cell differentiation, applying a statistical methodology to yield maximal in vitro TE differentiation, which was to be used in conjunction with the created constructs.

Together, the findings, methods and tools generated in this thesis contribute towards ongoing efforts to achieve sustainable, alternative production platforms for the creation of essential biomaterials.