Models of classroom assessment for course-based research experiences

Course-based research pedagogy involves positioning students as contributors to authentic research projects as part of an engaging educational experience that promotes their learning and persistence in science. To develop a model for assessing and grading students engaged in this type of learning experience, the assessment aims and practices of a community of experienced course-based research instructors were collected and analyzed. This approach defines four aims of course-based research assessment—(1) Assessing Laboratory Work and Scientific Thinking; (2) Evaluating Mastery of Concepts, Quantitative Thinking and Skills; (3) Appraising Forms of Scientific Communication; and (4) Metacognition of Learning—along with a set of practices for each aim. These aims and practices of assessment were then integrated with previously developed models of course-based research instruction to reveal an assessment program in which instructors provide extensive feedback to support productive student engagement in research while grading those aspects of research that are necessary for the student to succeed. Assessment conducted in this way delicately balances the need to facilitate students’ ongoing research with the requirement of a final grade without undercutting the important aims of a CRE education

Nuclear mutations specifically affect the synthesis and/or degradation of the chloroplast-encoded D2 polypeptide of photosystem II in <i>Chlamydomonas reinhardtii</i>

To study the interaction of the nuclear and chloroplast genomes in the biogenesis of the photosynthetic apparatus, nuclear mutants of Chlamydomonas reinhardtii deficient in photosystem II (PSII) activity were analyzed. Two independently-isolated, allelic nuclear mutants show a pleiotropic reduction in a set of functionally related PSII polypeptides. Immunoblot analysis reveals that the two mutants, nac-1-18 and nac-1-11, accumulate reduced amounts of the chloroplast-encoded polypeptides P5 and P6 and are completely deficient in polypeptides D1 and D2. Polypeptides of the oxygen-evolving and light-harvesting complexes associated with PSII, however, are present at wild-type levels. Analysis of mRNAs encoding PSII polypeptides from these mutants indicates that all messages are present, although some species, including the D2 message, are significantly elevated. When mutant cells are pulse-labeled for 10 min with [C]acetate, a greatly reduced amount of labeled D2 protein is observed, while all other PSII polypeptides are synthesized normally. These data indicate that the mutations present in nac-1-18 and nac-1-11 affect a nuclear gene whose product specifically controls the translation and/or degradation of the chloroplast-encoded D2 polypeptide

Nuclear mutations specifically affect the synthesis and/or degradation of the chloroplast-encoded D2 polypeptide of photosystem II in <i>Chlamydomonas reinhardtii</i>

To study the interaction of the nuclear and chloroplast genomes in the biogenesis of the photosynthetic apparatus, nuclear mutants of Chlamydomonas reinhardtii deficient in photosystem II (PSII) activity were analyzed. Two independently-isolated, allelic nuclear mutants show a pleiotropic reduction in a set of functionally related PSII polypeptides. Immunoblot analysis reveals that the two mutants, nac-1-18 and nac-1-11, accumulate reduced amounts of the chloroplast-encoded polypeptides P5 and P6 and are completely deficient in polypeptides D1 and D2. Polypeptides of the oxygen-evolving and light-harvesting complexes associated with PSII, however, are present at wild-type levels. Analysis of mRNAs encoding PSII polypeptides from these mutants indicates that all messages are present, although some species, including the D2 message, are significantly elevated. When mutant cells are pulse-labeled for 10 min with [C]acetate, a greatly reduced amount of labeled D2 protein is observed, while all other PSII polypeptides are synthesized normally. These data indicate that the mutations present in nac-1-18 and nac-1-11 affect a nuclear gene whose product specifically controls the translation and/or degradation of the chloroplast-encoded D2 polypeptide

Chloroplast Molecular Genetics of <i>Chlamydomonas</i>: a Tool for Studying the Function, Synthesis and Assembly of the Photosynthetic Apparatus

The green unicellular alga Chlamydomonas reinhardtii offers interesting possibilities for studying the function, synthesis and assembly of the photosynthetic apparatus. Chloroplast and nuclear genes coding for subunits of photosystem II, a major multimolecular membrane-associated photosynthetic complex, have been isolated and characterized. Examination of these genes and of their expression in wild-type cells and in chloroplast and nuclear photosystem II mutants has revealed a complex regulatory circuitry between chloroplast and nucleocytoplasmic compartments. One of the photosystem II subunits which is involved in herbicide binding has been found to have distinct single amino acid substitutions in several herbicide resistant mutants. Some of these mutations do not appreciably affect photosynthetic yield and may therefore be of agronomic interest

Chloroplast Molecular Genetics of <i>Chlamydomonas</i>: a Tool for Studying the Function, Synthesis and Assembly of the Photosynthetic Apparatus

The green unicellular alga Chlamydomonas reinhardtii offers interesting possibilities for studying the function, synthesis and assembly of the photosynthetic apparatus. Chloroplast and nuclear genes coding for subunits of photosystem II, a major multimolecular membrane-associated photosynthetic complex, have been isolated and characterized. Examination of these genes and of their expression in wild-type cells and in chloroplast and nuclear photosystem II mutants has revealed a complex regulatory circuitry between chloroplast and nucleocytoplasmic compartments. One of the photosystem II subunits which is involved in herbicide binding has been found to have distinct single amino acid substitutions in several herbicide resistant mutants. Some of these mutations do not appreciably affect photosynthetic yield and may therefore be of agronomic interest

Nuclear and chloroplast mutations affect the synthesis or stability of the chloroplast <i>psbC</i> gene product in <i>Chlamydomonas reinhardtii</i>

The psbC gene of Chlamydomonas reinhardtii encodes P6, the 43 kd photosystem II core polypeptide. The sequence of P6 is highly homologous to the corresponding protein in higher plants with the exception of the N-terminal region where the first 12 amino acids are missing. Translation of P6 is initiated at GUG in C. reinhardtii. The chloroplast mutant MA16 produces a highly unstable P6 protein. The mutation in this strain maps near the middle of the psbC gene and consists of a 6 bp duplication that creates a Ser-Leu repeat at the end of one transmembrane domain. Two nuclear mutants, F34 and F64, and one chloroplast mutant, FuD34, are unable to synthesize P6. All of these mutants accumulate wild-type levels of psbC mRNA. The FuD34 mutation has been localized near the middle of the 550 bp 5' untranslated region of psbC where the RNA can be folded into a stem-loop structure. A chloroplast suppressor of F34 has been isolated that partially restores synthesis of the 43 kd protein. The mutation of this suppressor is near that of FuD34, in the same stem-loop region. These chloroplast mutations appear to define the target site of a nuclear factor that is involved in P6 translation

PGRL1 Participates in Iron-induced Remodeling of the Photosynthetic Apparatus and in Energy Metabolism in Chlamydomonas reinhardtii*

PGRL1 RNA and protein levels are increased in iron-deficient Chlamydomonas reinhardtii cells. In an RNAi strain, which accumulates lower PGRL1 levels in both iron-replete and -starved conditions, the photosynthetic electron transfer rate is decreased, respiratory capacity in iron-sufficient conditions is increased, and the efficiency of cyclic electron transfer under iron-deprivation is diminished. Pgrl1-kd cells exhibit iron deficiency symptoms at higher iron concentrations than wild-type cells, although the cells are not more depleted in cellular iron relative to wild-type cells as measured by mass spectrometry. Thiol-trapping experiments indicate iron-dependent and redox-induced conformational changes in PGRL1 that may provide a link between iron metabolism and the partitioning of photosynthetic electron transfer between linear and cyclic flow. We propose, therefore, that PGRL1 in C. reinhardtii may possess a dual function in the chloroplast; that is, iron sensing and modulation of electron transfer