Shedding light on Arabidopsis seed lipid metabolism
In a recent The Plant Cell publication of the Zeeman lab (IMPB), Deslandes-Hérold and colleagues study the influence of a light-dependent biochemical pathway on seed oil accumulation using the Arabidopsis thaliana model system. They find a larger-than-anticipated effect of this pathway on the amount of oil accumulated and provide new insight into the metabolic partitioning of resources between seed storage compounds.
Light is the driver of photosynthesis in leaves, which underpins the whole of plant metabolism. However, some plants go further; the otherwise heterotrophic developing embryos of certain oilseed species are also green and capture light energy. The light filtering through the seedpod to the embryo is minimal. Nevertheless, it is thought to be sufficient to fuel reactions enhancing the efficiency by which sugars are converted to oil. This is proposed to be achieved by a subset of enzymes from different pathways (the oxidative pentose phosphate pathway and the Calvin-Benson Cycle), resulting in a non-canonical pathway - the ‘PRK/Rubisco shunt’. This pathway allows some carbon lost as CO2 during oil production to be recycled.
To study the importance of the PRK/Rubisco shunt genetically, Deslandes-Hérold et al. engineered Arabidopsis plants producing seeds that either can or cannot operate the shunt, all within the same pod. Comparing these seeds revealed that the PRK/Rubisco shunt contributes significantly to storage resource accumulation and that the pathway is tightly embedded into the seeds’ metabolism; blocking it had broad effects beyond just reducing oil accumulation. The work not only demonstrates that the proposed pathway is active in Arabidopsis seeds, but also that its importance may have been underestimated. This opens up a myriad of novel research questions and will leverage future approaches to increase carbon-use efficiency in commercially important oilseed crops.
Link to the paper in external page Plant Cell