Deciphering the Proteotoxic Stress Responses Triggered by the Perturbed Thylakoid Proteostasis in Arabidopsis.

Here, we explored heat dependent thylakoid FtsH protease substrates and investigated proteotoxicity induced by thermal damage and processive protease dysfunction on the thylakoid membrane. Through our thylakoid enriched proteome analysis and biochemical experiments, carbonylated stromal proteins were suggested as possible FtsH targets. Furthermore, we observed in the thylakoid fractions in the absence of FtsH stromal reactive oxygen species-detoxifying enzymes, as well as heat shock proteins and chaperones, which are known to be upregulated at the transcriptional level when this protease is absent, which is called the damaged protein response, resembling unfolded protein response in eukaryotic cells.

Fine-tuned regulation of the K /H antiporter KEA3 is required to optimize photosynthesis during induction.

KEA3 is a thylakoid membrane localized K /H antiporter that regulates photosynthesis by modulating two components of proton motive force (pmf), the proton gradient (∆pH) and the electric potential (∆ψ). We identified a mutant allele of KEA3, disturbed proton gradient regulation (dpgr) based on its reduced non-photochemical quenching (NPQ) in artificial (CO -free with low O ) air. This phenotype was enhanced in the mutant backgrounds of PSI cyclic electron transport (pgr5 and crr2-1).

Light harvesting and chloroplast electron transport in NADP-malic enzyme type C4 plants.

The structure of thylakoids in chloroplasts and the organization of the electron transport chain changed dynamically during the evolution of C4 photosynthesis, especially in the nicotinamide adenine dinucleotide phosphate (NADP)-malic enzyme type C4 species. Stacked grana membranes are strongly reduced in the bundle sheath chloroplasts of these plants, where photosystem II activity is diminished and cyclic electron transport around photosystem I mainly occurs. This change optimizes the ATP/NADPH production ratio in bundle sheath chloroplasts to drive the metabolic cycle of C4 photosynthesis.

Promotion of Cyclic Electron Transport Around Photosystem I with the Development of C4 Photosynthesis.

C4 photosynthesis is present in approximately 7,500 species classified into 19 families, including monocots and eudicots. In the majority of documented cases, a two-celled CO2-concentrating system that uses a metabolic cycle of four-carbon compounds is employed. C4 photosynthesis repeatedly evolved from C3 photosynthesis, possibly driven by the survival advantages it bestows in the hot, often dry, and nutrient-poor soils of the tropics and subtropics.

Distinct palisade tissue development processes promoted by leaf autonomous signalling and long-distance signalling in Arabidopsis thaliana.

Plants develop palisade tissue consisting of cylindrical mesophyll cells located at the adaxial side of leaves in response to high light. To understand high light signalling in palisade tissue development, we investigated leaf autonomous and long-distance signal responses of palisade tissue development using Arabidopsis thaliana. Illumination of a developing leaf with high light induced cell height elongation, whereas illumination of mature leaves with high light increased cell density and suppressed cell width expansion in palisade tissue of new leaves.

Promotion of cyclic electron transport around photosystem I during the evolution of NADP-malic enzyme-type C4 photosynthesis in the genus Flaveria.

C4 plants display higher cyclic electron transport activity than C3 plants. This activity is suggested to be important for the production of ATPs required for C4 metabolism. To understand the process by which photosystem I (PSI) cyclic electron transport was promoted during C4 evolution, we conducted comparative analyses of the functionality of PSI cyclic electron transport among members of the genus Flaveria, which contains several C3, C3-C4 intermediate, C4-like and C4 species.

Responses of the photosynthetic electron transport system to excess light energy caused by water deficit in wild watermelon.

In plants, drought stress coupled with high levels of illumination causes not only dehydration of tissues, but also oxidative damage resulting from excess absorbed light energy. In this study, we analyzed the regulation of electron transport under drought/high-light stress conditions in wild watermelon, a xerophyte that shows strong resistance to this type of stress. Under drought/high-light conditions that completely suppressed CO(2) fixation, the linear electron flow was diminished between photosystem (PS) II and PS I, there was no photoinhibitory damage to PS II and PS I and no decrease in the abundance of the two PSs.

Elevated expression of PGR5 and NDH-H in bundle sheath chloroplasts in C4 flaveria species.

Cyclic electron transport around PSI has been proposed to supply the additional ATP required for C(4) photosynthesis. To investigate the nature of cyclic electron pathways involved in C(4) photosynthesis, we analyzed tissue-specific expression of PGR5 (PROTON GRADIENT REGULATION 5), which is involved in the antimycin A-sensitive pathway, and NDH-H, a subunit of the plastidial NAD(P)H dehydrogenase complex, in four Flaveria species comprising NADP-malic enzyme (ME)-type C(4), C(3)-C(4) intermediate and C(3) species. PGR5 was highly expressed in the C(4) species and enriched in bundle sheath chloroplasts together with NDH-H, suggesting that electron transport of both PGR5-dependent and NDH-dependent cyclic pathways is promoted to drive C(4) photosynthesis.

The long-term responses of the photosynthetic proton circuit to drought.

Proton motive force (pmf) across thylakoid membranes is not only for harnessing solar energy for photosynthetic CO(2) fixation, but also for triggering feedback regulation of photosystem II antenna. The mechanisms for balancing these two roles of the proton circuit under the long-term environmental stress, such as prolonged drought, have been poorly understood. In this study, we report on the response of wild watermelon thylakoid 'proton circuit' to drought stress using both in vivo spectroscopy and molecular analyses of the representative photosynthetic components.

Effect of PGR5 impairment on photosynthesis and growth in Arabidopsis thaliana.

PGR5 has been reported as an important factor for the activity of the ferredoxin-dependent cyclic electron transport around PSI. To elucidate the role of PGR5 in C(3) photosynthesis, we characterized the photosynthetic electron transport rate (ETR), CO(2) assimilation and growth in the Arabidopsis thaliana pgr5 mutant at various irradiances and with CO(2) regimes. In low-light-grown pgr5, the CO(2) assimilation rate and ETR were similar to the those of the wild type at low irradiance, but decreased at saturating irradiance under photorespiratory conditions as well as non-photorespiratory conditions.