Regulation of carbon-concentrating mechanism and oil production in a g…

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  • 2017-01-06


[2016 Fall Life Sciences & IBB Regular Seminar]
                      ▶Subject: Regulation of carbon-concentrating mechanism and oil production in a green alga, Chlamydomonas reinhardtii
                      ▶Speaker: Prof. Hideya Fukuzawa (Laboratory of Applied Molecular Microbiology, Graduate School of Biostudies, Kyoto University)
                      ▶Date: 4:30PM/Nov. 11(Fri.)/2016
                      ▶Place: Auditorium(1F), POSTECH Biotech Center
                      Part 1. Chloroplast-mediated regulation of CO2-concentrating mechanism by Ca2+-binding protein CAS in the green alga Chlamydomonas reinhardtii
 Aquatic photosynthetic organisms, including the green alga Chlamydomonas reinhardtii, induce a CO2-concentrating mechanism (CCM) to maintain photosynthetic activity in CO2-limiting conditions by sensing environmental CO2 and light availability. Previously, a novel high-CO2-requiring mutant, H82, defective in the induction of the CCM was isolated. A homolog of calcium (Ca2+)-binding protein CAS, originally found in Arabidopsis thaliana, was disrupted in H82 cells. Although Arabidopsis CAS is reported to be associated with stomatal closure or immune responses via a chloroplast-mediated retrograde signal, the relationship between a Ca2+ signal and the CCM associated with the function of CAS in an aquatic environment are still unclear. In this study, the introduction of an intact CAS gene into H82 cells restored photosynthetic affinity for inorganic carbon, and RNA-seq analyses revealed that CAS could function in maintaining the expression levels of nuclear-encoded CO2-limiting-inducible genes, including the HCO3– transporters HLA3 and LCIA. CAS changed its localization from dispersed across the thylakoid membrane in high-CO2 conditions or in the dark to being associated with tubule-like structures in the pyrenoid in CO2-limiting conditions along with a significant increase of the fluorescent signals of the Ca2+ indicator in the pyrenoid. Chlamydomonas CAS had Ca2+-binding activity and the perturbation of intracellular Ca2+ homeostasis by a Ca2+-chelator or calmodulin antagonist impaired the accumulation of HLA3 and LCIA. These results suggested that Chlamydomonas CAS is a novel Ca2+-mediated regulator of CCM-related genes via a retrograde signal from the pyrenoid in the chloroplast to the nucleus.
 PNAS in press. DOI: 10.1073/pnas.1606519113
 Part 2: Algal Dual-Specificity Tyrosine-Phosphorylation-Regulated Kinase TAR1 Regulates Accumulation of Triacylglycerol in Nitrogen- or Sulfur-Deficiency
 Although microalgae accumulate triacylglycerol (TAG) and starch in response to
 nutrient-deficient conditions, the regulatory mechanisms are poorly understood. We report here the identification and characterization of a kinase, TAG accumulation regulator 1(TAR1), which is a member of the yeast Yak1 subfamily in the dual-specificity tyrosine-phosphorylation-regulated kinase family in a green alga, Chlamydomonas reinhardtii. The kinase domain of TAR1 demonstrated auto- and trans-phosphorylation activities. A TAR1-defective mutant, tar1-1, accumulated TAG to levels 0.6-fold and 0.2-fold of those of a wild-type strain in sulfur (S)- and nitrogen (N)-deficient conditions, respectively. In N-deficient conditions, tar1-1 arrested cell division, increased cell size and cell dry weight, and maintained chlorophyll and photosynthetic activity, which were not observed in S-deficient conditions. In N-deficient conditions, global changes in expression levels of N-deficiency responsive genes in N assimilation and tetrapyrrole metabolism were noted between tar1-1 and wild-type cells. These results indicated that TAR1 is a regulator of TAG accumulation in S- and N-deficient conditions, and it functions in cell growth and repression of photosynthesis in conditions of N deficiency. Further analyses under autotrophic conditions will be presented.
Plant Physiol. 2015 Jun;168(2):752-764. 

                  ▶Inquiry: Prof. Youngsook Lee (T. 279-2296)
                        * This seminar will be given in English.
                    please refrain from taking photos during seminars. *