Summary: The mutants irt1‐1 and irt1‐2 of Arabidopsis thaliana were identified among a collection of T‐DNA‐tagged lines on the basis of a decrease in the effective quantum yield of photosystem II. The mutations responsible interfere with expression of IRT1, a nuclear gene that encodes the metal ion transporter IRT1. In irt1 mutants, photosensitivity and chlorophyll fluorescence parameters, as well as abundance and composition of the photosynthetic apparatus, are significantly altered. Additional effects of the mutation under greenhouse conditions, including chlorosis and a drastic reduction in growth rate and fertility, are compatible with a deficiency in iron transport. Propagation of irt1 plants on media supplemented with additional quantities of iron salts restores almost all aspects of wild‐type behaviour. The irt2‐1 mutant, which carries an En insertion in the highly homologous IRT2 gene of Arabidopsis thaliana, was identified by reverse genetics and shows no symptoms of iron deficiency. This, together with the finding that irt1‐1 can be complemented by 35S::IRT1 but not by 35S::IRT2, demonstrates that, although the products of the two genes are closely related, only AtIRT1 is required for iron homeostasis under physiological conditions.

The chromophore binding properties of the higher plant light-harvesting complex II have been studied by site-directed mutagenesis of pigment-binding residues. Mutant apoproteins were overexpressed in Escherichia coli and then refoldedin vitro with purified chromophores to yield holoproteins selectively affected in chlorophyll-binding sites. Biochemical and spectroscopic characterization showed a specific loss of pigments and absorption spectral forms for each mutant, thus allowing identification of the chromophores bound to most of the binding sites. On these bases a map for the occupancy of individual sites by chlorophyll a and chlorophyll b is proposed. In some cases a single mutation led to the loss of more than one chromophore indicating that four chlorophylls and one xanthophyll could be bound by pigment-pigment interactions. Differential absorption spectroscopy allowed identification of the Q_y transition energy level for each chlorophyll within the complex. It is shown that not only site selectivity is largely conserved between light-harvesting complex II and CP29 but also the distribution of absorption forms among different protein domains, suggesting conservation of energy transfer pathways within the protein and outward to neighbor subunits of the photosystem.

Drosophilid fruit flies have provided science with striking cases of behavioral adaptation and genetic innovation. A recent example is the invasive pest Drosophila suzukii, which, unlike most other Drosophila, lays eggs and feeds on undamaged, ripening fruits. This not only poses a serious threat for fruit cultivation but also offers an interesting model to study evolution of behavioral innovation. We developed genome and transcriptome resources for D. suzukii. Coupling analyses of these data with field observations, we propose a hypothesis of the origin of its peculiar ecology. Using nuclear and mitochondrial phylogenetic analyses, we confirm its Asian origin and reveal a surprising sister relationship between the eugracilis and the melanogaster subgroups. Although the D. suzukii genome is comparable in size and repeat content to other Drosophila species, it has the lowest nucleotide substitution rate among the species analyzed in this study. This finding is compatible with the overwintering diapause of D. suzukii, which results in a reduced number of generations per year compared with its sister species. Genome-scale relaxed clock analyses support a late Miocene origin of D. suzukii, concomitant with paleogeological and climatic conditions that suggest an adaptation to temperate montane forests, a hypothesis confirmed by field trapping. We propose a causal link between the ecological adaptations of D. suzukii in its native habitat and its invasive success in Europe and North America.

Plastocyanin is a soluble copper-containing protein present in the thylakoid lumen, which transfers electrons to photosystem I. In the chloroplast of the flowering plant Arabidopsis thaliana, a cytochrome c₆-like protein is present, which was recently suggested to function as an alternative electron carrier to plastocyanin. We show that Arabidopsis plants mutated in both of the two plastocyanin-coding genes and with a functional cytochrome c₆ cannot grow photoautotrophically because of a complete block in light-driven electron transport. Even increased dosage of the gene encoding the cytochrome c₆-like protein cannot complement the double mutant phenotype. This demonstrates that in Arabidopsis only plastocyanin can donate electrons to photosystem I in vivo.

Summary: In Arabidopsis thaliana, the D‐subunit of photosystem I (PSI‐D) is encoded by two functional genes, PsaD1 and PsaD2, which are highly homologous. Knock‐out alleles for each of the loci have been identified by a combination of forward and reverse genetics. The double mutant psad1‐1 psad2‐1 is seedling‐lethal, high‐chlorophyll‐fluorescent and deficient for all tested PSI subunits, indicating that PSI‐D is essential for photosynthesis. In addition, psad1‐1 psad2‐1 plants show a defect in the accumulation of thylakoid multiprotein complexes other than PSI. Of the single‐gene mutations, psad2 plants behave like wild‐type (WT) plants, whereas psad1‐1 markedly affects the accumulation of PsaD mRNA and protein, and photosynthetic electron flow. Additional effects of the psad1‐1 mutation include a decrease in growth rate under greenhouse conditions and downregulation of the mRNA expression of most genes involved in the light phase of photosynthesis. In the same mutant, a marked decrease in the levels of PSI and PSII polypeptides is evident, as well as a light‐green leaf coloration and increased photosensitivity. Increased dosage of PsaD2 in the psad1‐1 background restores the WT phenotype, indicating that PSI‐D1 and PSI‐D2 have redundant functions.