Leif Pallesen
Meeting the global food and energy demands in the coming decades will require innovative and sustainable solutions. Both food and biofuel require photosynthesis to harness abundant solar energy and store it in biomass via carbon fixation. The efficiency of photosynthesis is often limited by the availability of CO2. Interestingly, the alga Chlamydomonas reinhardtii enhances photosynthetic efficiency with a genetically encoded Carbon Concentrating Mechanism (CCM) that actively concentrates inorganic carbon (CO2 and HCO3-) inside the cell. The specific objective of this research is to comprehensively identify the genes required for photosynthesis and a subset constituting the CCM. Toward this end, we have developed a quantitative high-throughput growth phenotyping pipeline. We have screened >120,000 mutant stains and isolated several thousand with deficient photosynthetic growth in air. A functional CCM is required for efficient phototrophic growth in air, but not at elevated CO2 levels (ie. 3% CO2). As such, several hundred candidate CCM mutants were identified that exhibit deficient phototrophic growth in air (0.04% CO2) (CCM dependent) that is rescued by 3% CO2 (CCM independent). A deep-sequencing based approach was used to identify the mutation sites of strains of interest. The comprehensive identification of photosynthesis and CCM genes expands our understanding of these processes and opens the door to engineering more efficient plant crops for increased food and biofuel production.
Eunkyoo Oh
In plants, cell elongation and seedling morphogenesis are controlled by multiple environmental factors and endogenous hormones. How these signals regulate largely overlapping cellular and physiological responses through distinct signalling pathways remains an outstanding question in plant biology. I will illustrate a molecular network that integrates all major growth-regulating signals, including auxin, Brassinosteroid (BR), gibberellin (GA), light, and temperature. Analyses of genome-wide targets, genetic and biochemical interactions demonstrate that the auxin-response factor ARF6, the light/temperature-regulated transcription factor PIF4, and the BR-signaling transcription factor BZR1, interact with each other, and cooperatively regulate large numbers of common target genes and hypocotyl elongation. However, their DNA-binding activities are blocked by the GA-inactivated repressor RGA and GA-promoted hypocotyl elongation requires these transcription factors activities. In the downstream of the ARF6-PIF4-BZR1 module, the PRE family helix-loop-helix factors promote hypocotyl elongation. These results demonstrate a central molecular network that integrates multiple hormonal and environmental signals for regulating cell elongation in the Arabidopsis hypocotyl.