Big progress for small subunits: new Rubisco mutants in Arabidopsis

Nearly 75 years after Rubisco was first isolated from spinach leaves, the enzyme's function and regulation remain an important research topic and longstanding target to improve plant productivity. In plants, Rubisco is a complex made up of eight large subunits (LSUs) encoded in the chloroplast genome (rbcL), while eight small subunits (SSUs) are encoded in the nucleus as a multi-rbcS gene family. Despite decades of investigation, the function and interaction of the different small subunits in plant Rubisco remain enigmatic. Khumsupan et al. (2020) have used CRISPR/Cas9 [clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9] and T-DNA insertion lines within Arabidopsis thaliana to generate a suite of single and multiple gene knockout mutants for the four rbcS members. This enabled characterization of the homogenous Rubisco pool consisting of a single SSU isoform in planta. In doing so, they provide a powerful toolkit to expand our understanding of Rubisco structure-function relationships inside the leaf.