Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Root Biosynthesis Engineering of the “Plant Diamond” Sporopollenin for Permanent Belowground Carbon Storage

Authors:

Matias Kirst1* (mkirst@ufl.edu), Teagen Quilichini2

Institutions:

1University of Florida–Gainesville; 2National Research Council of Canada

Goals

The goals of this project are to (1) identify the genes required for sporopollenin synthesis and deposition and (2) introduce their expression in Populus to engineer sporopollenin production in roots as a stable carbon (C) sink.

Abstract

This recently funded project is part of the DOE Carbon Negative Shot™ Program, which calls for research on atmospheric carbon dioxide (CO2) removal and storage. To increase C storage, researchers propose to engineer the production of sporopollenin—the most recalcitrant plant polymer known (biostable for centuries or more vs. decades for other biopolymers)—in roots of bioenergy crops. Researchers will target Populus species since these trees are among DOE’s most important crops to be used for bioenergy.

In the first part of this project, the team will attempt to synthesize sporopollenin in Populus root epidermal cells, based on current knowledge of sporopollenin synthesis genes and epidermis- specific regulation of gene expression. More specifically, researchers will induce the expression of the presently known core set of enzymes needed to synthesize sporopollenin precursors—the Populus orthologs of ACOS5, PKSA, PKSB, TKPR1, and MS2 and the proposed master transcription factor regulators of sporopollenin synthesis AMS and MS188. Gene constructs driven by a root epidermis-specific promoter will be introduced into Populus via hairy root transformation of in vitro-grown shoots with Agrobacterium rhizogenes.

The second component of this project will use single-cell genomics to uncover genes that are activated during tapetum development and sporopollenin synthesis in Arabidopsis and Populus. Researchers’ aim is to identify regulatory genes involved in this process that have not yet been characterized and define evolutionarily conserved genetic mechanisms of sporopollenin synthesis, which is likely to be essential for the transfer of this cellular role to other cell types or species. The team will validate the function of these genes in Arabidopsis before adding them to the Populus genetic toolkit developed in the first part of this project.

The proposed strategy, deployed at scale, has the potential to strip substantial amounts of C from the atmosphere. Based on typical Populus biomass yields and allocation belowground, engineering roots to contain 5% by weight sporopollenin could permanently store 120 to 300 kg CO2-equivalents per hectare per year or 96 to 2,400 kg per hectare in an 8-year cycle. Researchers estimate that engineering the 36-million-hectare U.S. maize crop to accumulate 5% sporopollenin in roots and stover could sequester ~50 megatons of CO2-equivalents per year, or ~0.5 gigatons per decade.

Funding Information

This research is part of the DOE Energy Earthshots™, Carbon Negative Shots Program supported by the DOE Office of Science, BER program, grant no. DE-SC0024708.