Orchestration Of Photosynthesis-associated Gene Expression And Galactolipid Biosynthesis During Chloroplast Differentiation In Plants.

The chloroplast thylakoid membrane is composed of membrane lipids and photosynthetic protein complexes, and orchestration of thylakoid lipid biosynthesis and photosynthesis-associated protein accumulation is considered important for thylakoid development. Galactolipids consist of ~80% of the thylakoid lipids and their biosynthesis is fundamental for chloroplast development. We previously reported that the suppression of galactolipid biosynthesis decreased the expression of photosynthesis-associated nuclear- and plastid-encoded genes (PhANGs and PhAPGs). However, the mechanism for coordinative regulation between galactolipid biosynthesis in plastids and expression of PhANGs and PhAPGs remains largely unknown. To elucidate this mechanism, we investigated the gene expression patterns in galactolipid-deficient Arabidopsis seedlings during the deetiolation process. We found that galactolipids are crucial for inducing both the transcript accumulation of PhANGs and PhAPGs and the accumulation of plastid-encoded photosynthesis-associated proteins in developing chloroplasts. Genetic analysis indicates the contribution of GENOMES UNCOUPLED1 (GUN1)-mediated plastid-to-nucleus signaling pathway for PhANG regulation in response to galactolipid levels. Previous studies suggested that the accumulation of GUN1 reflects the state of protein homeostasis in plastids and alters the PhANG expression level. Thus we propose a model that galactolipid biosynthesis determines the protein homeostasis in plastids at the initial phase of deetiolation and optimizes the GUN1-dependent signaling to regulate the PhANG expression. This mechanism might contribute to orchestrating the biosynthesis of lipids and proteins for the biogenesis of functional chloroplasts in plants.

High myristic acid in glycerolipids enhances the repair of photodamaged photosystem II under strong light.

Cyanobacteria inhabit areas with a broad range of light, temperature, and nutrient conditions. The robustness of cyanobacterial cells, which can survive under different conditions, may depend on the resilience of photosynthetic activity. Cyanothece sp. PCC 8801 (Cyanothece), a freshwater cyanobacterium isolated from a Taiwanese rice field, had a higher repair activity of photodamaged photosystem II (PSII) under intense light than Synechocystis sp. PCC 6803 (Synechocystis), another freshwater cyanobacterium. Cyanothece contains myristic acid (14:0) as the major fatty acid at the sn-2 position of the glycerolipids. To investigate the role of 14:0 in the repair of photodamaged PSII, we used a Synechocystis transformant expressing a T-1274 encoding a lysophosphatidic acid acyltransferase (LPAAT) from Cyanothece. The wild-type and transformant cells contained 0.2 and 20.1 mol% of 14:0 in glycerolipids, respectively. The higher content of 14:0 in the transformants increased the fluidity of the thylakoid membrane. In the transformants, PSII repair was accelerated due to an enhancement in the de novo synthesis of D1 protein, and the production of singlet oxygen (1O2), which inhibited protein synthesis, was suppressed. The high content of 14:0 increased transfer of light energy received by phycobilisomes to PSI and CP47 in PSII and the content of carotenoids. These results indicated that an increase in 14:0 reduced 1O2 formation and enhanced PSII repair. The higher content of 14:0 in the glycerolipids may be required as a survival strategy for Cyanothece inhabiting a rice field under direct sunlight.

Comparison of Early Postoperative Diffusion Weighted Magnetic Resonance Imaging Findings After Resection of Gliomas and Meningiomas.

OBJECTIVE: Glioma and meningioma require vastly different surgical approaches, even if only involving a simple craniotomy procedure. Diffusion weighted imaging (DWI) is useful for the postoperative evaluation of ischemic damage. The present study evaluated the expected but unproven differences in DWI findings. METHODS: A total of 41 patients with meningiomas and 63 with gliomas met the inclusion criteria for adult cases with superficial lesions treated through simple supratentorial craniotomy. Postoperative DWI findings of DWI-positive rate, DWI-positive area type, and relationship with neurological deficits were evaluated. RESULTS: The DWI-positive rate (P = 0.01) and the proportion of rim-type lesions (P < 0.01) were significantly more common in gliomas. Patients with meningiomas and DWI-positive areas presented with higher rates of new neurological deficits (P < 0.01), and patients with meningiomas on the left side were more likely to develop new neurological deficits (P = 0.02). Patients with gliomas tended to develop new deficits with larger DWI-positive area volumes (P = 0.04). CONCLUSIONS: Postoperative early DWI-positive rate and rim-type lesions are more common after glioma resection than meningioma resection. Larger volumes of DWI-positive areas may be associated with postoperative neurological symptoms in gliomas. DWI-positive finding is less common after meningioma than glioma resection but more likely to be associated with new neurological symptoms. These differences are important for adequate postoperative DWI evaluation of common supratentorial brain tumors.

Biosynthesis of phosphatidylglycerol in photosynthetic organisms.

Phosphatidylglycerol (PG) is a unique phospholipid class with its indispensable role in photosynthesis and growth in land plants, algae, and cyanobacteria. PG is the only major phospholipid in the thylakoid membrane of cyanobacteria and plant chloroplasts and a main lipid component in photosynthetic protein-cofactor complexes such as photosystem I and photosystem II. In plants and algae, PG is also essential as a substrate for the biosynthesis of cardiolipin, which is a unique lipid present only in mitochondrial membranes and crucial for the functions of mitochondria. PG biosynthesis pathways in plants include three membranous organelles, plastids, mitochondria, and the endoplasmic reticulum in a complex manner. While the molecular biology underlying the role of PG in photosynthetic functions is well established, many enzymes responsible for the PG biosynthesis are only recently cloned and functionally characterized in the model plant species including Arabidopsis thaliana and Chlamydomonas reinhardtii and cyanobacteria such as Synechocystis sp. PCC 6803. The characterization of those enzymes helps understand not only the metabolic flow for PG production but also the crosstalk of biosynthesis pathways between PG and other lipids. This review aims to summarize recent advances in the understanding of the PG biosynthesis pathway and functions of involved enzymes.

Anionic lipids facilitate membrane development and protochlorophyllide biosynthesis in etioplasts.

Dark-germinated angiosperm seedlings develop chloroplast precursors called etioplasts in cotyledon cells. Etioplasts develop lattice membrane structures called prolamellar bodies (PLBs), where the chlorophyll intermediate protochlorophyllide (Pchlide) forms a ternary complex with NADPH and light-dependent NADPH:Pchlide oxidoreductase (LPOR). The lipid bilayers of etioplast membranes are mainly composed of galactolipids, which play important roles in membrane-associated processes in etioplasts. Although etioplast membranes also contain 2 anionic lipids, phosphatidylglycerol (PG) and sulfoquinovosyldiacylglycerol (SQDG), their roles are unknown. To determine the roles of PG and SQDG in etioplast development, we characterized etiolated Arabidopsis (Arabidopsis thaliana) mutants deficient in PG and SQDG biosynthesis. A partial deficiency in PG biosynthesis loosened the lattice structure of PLBs and impaired the insertion of Mg2+ into protoporphyrin IX, leading to a substantial decrease in Pchlide content. Although a complete lack of SQDG biosynthesis did not notably affect PLB formation and Pchlide biosynthesis, lack of SQDG in addition to partial PG deficiency strongly impaired these processes. These results suggested that PG is required for PLB formation and Pchlide biosynthesis, whereas SQDG plays an auxiliary role in these processes. Notably, PG deficiency and lack of SQDG oppositely affected the dynamics of LPOR complexes after photoconversion, suggesting different involvements of PG and SQDG in LPOR complex organization. Our data demonstrate pleiotropic roles of anionic lipids in etioplast development.

Deacylation of galactolipids decomposes photosystem II dimers to enhance degradation of damaged D1 protein.

Photosystem II (PSII) contains many lipid molecules that are essential for the function and maintenance of PSII. Under strong light conditions, PSII complexes are dynamically modified during the repair process; however, the molecular mechanism of the dynamic changes in the PSII structure is still unclear. In the present study, we investigated the role of a lipase in the repair of PSII in Synechocystis sp. PCC 6803. We identified a protein encoded by the sll1969 gene, previously named lipase A (lipA), in the Synechocystis sp. PCC 6803 genome as a candidate for the lipase involved in PSII repair. Recombinant protein expressed in Escherichia coli cells hydrolyzed fatty acids at the sn-1 position of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol as well as triacylglycerol esterified with stearic acids. PSII repair in a disrupted mutant of the lipA gene was suppressed by the slow degradation of damaged D1 protein under strong light. The level of the PSII dimer remained higher in lipA mutant cells than wild-type (WT) cells under strong light. LipA protein was associated with the PSII dimer in vivo, and recombinant LipA protein decomposed PSII dimers purified from WT cells to monomers by reducing MGDG content in the PSII complex. These results indicate that LipA reacts with PSII dimers, dissociates them into monomers by digesting MGDG, and enhances D1 degradation during PSII repair.

Evaluation of Occluded Distal Vessels with Variable Flip-Angle 3-Dimensional Turbo Spin-Echo Magnetic Resonance Imaging Before Acute Mechanical Thrombectomy.

OBJECTIVE: The aim of this study was to evaluate the course of occluded distal vessels before mechanical thrombectomy (MT) for acute large vessel occlusion (LVO) with non-contrast magnetic resonance imaging (MRI). The variable flip-angle three-dimensional turbo spin-echo (VRFA-3D-TSE) method was used to evaluate the course of occluded distal vessels quickly and clearly in acute LVO cases before MT. METHODS: Patients with acute LVO who were indicated for MT between April 2021 and March 2022 were examined by the VRFA-3D-TSE method to evaluate the distal course of occluded vessels. We included internal carotid artery (ICA) occlusion, M1 occlusion of the middle cerebral artery, and basilar artery (BA) occlusion. Preoperative images were compared to the angiographic findings after recanalization or with follow-up magnetic resonance angiography, and the results were assessed by 2 endovascular treatment specialists as excellent, good, or poor imaging. RESULTS: MT was performed in a total of 27 patients. There were 17 patients with intracranial occlusion of the ICA, M1, and BA. Occlusion was found in the intracranial ICA in 6 patients, the M1 in 7, and the BA in 4. VRFA-3D-TSE MRI was performed in all patients, and the imaging was rated (by the 2assessors) as excellent in 12 of 17 and 14 of 17 cases, good in 5 of 17 and 3 of 17 cases, and poor in 0 of 17 cases. CONCLUSIONS: In patients with acute LVO, VRFA-3D-TSE MRI enabled rapid and good depiction of the course of occluded distal vessels before MT without the use of contrast medium.

Impacts of phosphatidylglycerol on plastid gene expression and light induction of nuclear photosynthetic genes.

Phosphatidylglycerol (PG) is the only major phospholipid in the thylakoid membrane of chloroplasts. PG is essential for photosynthesis, and loss of PG in Arabidopsis thaliana results in severe defects of growth and chloroplast development, with decreased chlorophyll accumulation, impaired thylakoid formation, and down-regulation of photosynthesis-associated genes encoded in nuclear and plastid genomes. However, how the absence of PG affects gene expression and plant growth remains unclear. To elucidate this mechanism, we investigated transcriptional profiles of a PG-deficient Arabidopsis mutant pgp1-2 under various light conditions. Microarray analysis demonstrated that reactive oxygen species (ROS)-responsive genes were up-regulated in pgp1-2. However, ROS production was not enhanced in the mutant even under strong light, indicating limited impacts of photooxidative stress on the defects of pgp1-2. Illumination to dark-adapted pgp1-2 triggered down-regulation of photosynthesis-associated nuclear-encoded genes (PhANGs), while plastid-encoded genes were constantly suppressed. Overexpression of GOLDEN2-LIKE1 (GLK1), a transcription factor gene regulating chloroplast development, in pgp1-2 up-regulated PhANGs but not plastid-encoded genes along with chlorophyll accumulation. Our data suggest a broad impact of PG biosynthesis on nuclear-encoded genes partially via GLK1 and a specific involvement of this lipid in plastid gene expression and plant development.

Crucial importance of length of fatty-acyl chains bound to the sn-2 position of phosphatidylglycerol for growth and photosynthesis of Synechocystis sp. PCC 6803.

Phosphatidylglycerol (PG) in thylakoid membrane is essential for growth and photosynthesis of photosynthetic organisms. Although the sn-2 position of PG in thylakoid membrane is exclusively esterified with C16 fatty acids, the functional importance of the C16 fatty-acyl chains at the sn-2 position has not been clarified. In this study, we chemically synthesized non-metabolizable PG molecules: we introduced linoleic acid (18:2, fatty acid containing 18 carbons with 2 double bonds) and one of the saturated fatty acids with different chain length (12:0, 14:0, 16:0, 18:0 and 20:0) by ether linkage to the sn-1 and sn-2 positions, respectively. With the synthesized ether-linked PG molecules, we checked whether they could complement the growth and photosynthesis of pgsA mutant cells of Synechocystis sp. PCC 6803 to understand the importance of length of fatty chains at the sn-2 position of PG. The pgsA mutant is incapable of synthesizing PG, so it requires exogenous PG added to medium for growth. The growth rate and photosynthetic activity of mutant cells depended on the length of fatty chains: the PG molecular species binding 16:0 most effectively complemented the growth and photosynthesis of mutant cells, and other PG molecular species with fatty chains shorter or longer than 16:0 were less effective; especially, those binding 12:0 inhibited the growth and photosynthetic activity of the mutant cells. These data demonstrate that length of fatty chains bound to the sn-2 position of PG is critical for PG performance in growth and photosynthesis.

Effects of clinical outcomes by modification of patient selection protocol based on premorbid independence for mechanical thrombectomy in older adult patients.

OBJECTIVES: Since the beneficial effect attained by mechanical thrombectomy (MT) seems to be worse in older than in the younger population, the establishment of an ideal and distinctive patient selection protocol in older is warranted. Herein, we modified our patient selection protocol based on age and premorbid independence in older adult patients. MATERIALS AND METHODS: We retrospectively reviewed 141 consecutive patients with acute ischemic stroke who were treated with MT between 2015 and 2020. We started to restrict the indication of MT in very old patients (≥85-year-old) with severe premorbid functional independence (≥modified Rankin Scale [mRS] 3) in 2018. Clinical outcomes before the modification of protocol (period 1) were compared to after (period 2). RESULTS: Although there were no significant differences in median mRS at 90 days and the rates of favorable outcomes (mRS 0-2) between both periods, rates of poor outcomes (mRS 5, 6) significantly decreased (37.3% vs. 19.7%, P = 0.021) during period 2 compared with period 1. For older adults (≥80-year-old), median mRS was significantly better (P = 0.012) during period 2 than period 1. During period 1, rates of favorable outcomes were significantly lower (P = 0.004) in older than in younger. However, this significant difference was diminished (P = 0.28) during period 2. CONCLUSION: Our modified patient selection protocol in older adults, not only limited by age but also premorbid function, improved the therapeutic outcome of MT. In rapidly aging society, further investigations facilitating a better understanding are necessary to establish an optimal patient selection protocol.

Specific Incorporation of Polyunsaturated Fatty Acids into the sn-2 Position of Phosphatidylglycerol Accelerates Photodamage to Photosystem II under Strong Light.

Free fatty acids (FFAs) are generated by the reaction of lipases with membrane lipids. Generated polyunsaturated fatty acids (PUFAs) containing more than two double bonds have toxic effects in photosynthetic organisms. In the present study, we examined the effect of exogenous FFAs in the growth medium on the activity of photosystem II (PSII) under strong light in the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). PUFAs but not monounsaturated fatty acids accelerated the rate of photodamage to PSII by inactivating electron transfer at the oxygen-evolving complex. Moreover, supplemented PUFAs were specifically incorporated into the sn-2 position of phosphatidylglycerol (PG), which usually contains C16 fatty acids at the sn-2 position in Synechocystis cells. The disruption of the gene for an acyl-ACP synthetase reduced the effect of PUFAs on the photoinhibition of PSII. Thus, the specific incorporation of PUFAs into PG molecules requires acyl-ACP synthetase and leads to an unstable PSII, thereby accelerating photodamage to PSII. Our results are a breakthrough into elucidating the molecular mechanism of the toxicity of PUFAs to photosynthetic organisms.

ADAPT First-Line Strategy for MCA Mainstem Occlusion; Analysis for Optimal Salvage Therapy and its Related Factor.

OBJECTIVES: A direct first-pass aspiration technique (ADAPT) is an attractive interventional technique for mechanical thrombectomy (MT), which could achieve recanalization quickly and safely at a small amount of material resources. To clarify its usefulness, our ADAPT first-line strategy for middle cerebral artery (MCA)-mainstem occlusion was retrospectively analyzed. MATERIALS AND METHODS: We reviewed 54 consecutive patients who underwent MT for MCA-mainstem occlusion using ADAPT first-line strategy. A salvage procedure was concurrently conducted in cases that failed to achieve successful recanalization by ADAPT attempt alone. Procedural and clinical outcome were assessed in both ADAPT alone and Salvage groups. Further investigation was performed in cases that required salvage procedure to determine the reason, risk factors, and optimal procedure. RESULTS: Forty-one patients (75.9%) were able to achieve successful recanalization with ADAPT technique alone. In salvage group, the procedural time was longer, and rates of successful recanalization were lower than in ADAPT-alone group. No significant difference in the rates of favorable outcomes was observed. Among 13 patients who required salvage therapy, the major reason (eight cases) was intra-procedural "thrombus distal migration". Failure of recanalization was seen in two cases due to "inaccessibility". In patients who had "thrombus distal migration", occlusion in the proximal portion was more frequently observed than in patients who did not (p = 0.032, 63.6% vs. 23.3%). CONCLUSIONS: Our ADAPT first-line strategy for MCA-mainstem occlusion demonstrated favorable procedural and clinical outcomes, even in cases that required additional procedures. Further investigation and better understanding are required to refine this promising procedure.

A Direct Aspiration First Pass Technique for Vertebra-Basilar Occlusion: A Retrospective Comparison to Stent Retriever.

OBJECTIVES: This study aimed to assess the clinical usefulness of a direct aspiration first pass technique as a first-line strategy for mechanical thrombectomy in posterior circulation. MATERIALS AND METHODS: We examined 34 consecutive patients treated with mechanical thrombectomy for acute vertebrobasilar artery occlusion. Procedural and clinical outcomes were assessed and compared between patients treated with a direct aspiration first pass technique first-line strategy (ADAPT group) and stent retriever system first-line strategy (stent retriever group). RESULTS: Overall, successful reperfusion, complete reperfusion, and first-pass effects were achieved in 94.1%, 61.8%, and 50% of patients with acute ischemic stroke in vertebra-basilar artery occlusion treated with mechanical thrombectomy, respectively. The ADAPT group required a significantly shorter procedural time (p=.015) and fewer attempts (p=.0498) to achieve successful recanalization than the stent retriever group. The ADAPT group also tended to show better recanalization rates and first-pass effects than the stent retriever group. The rates of favorable outcomes seemed to be better, although insignificant, in the ADAPT group than in the stent retriever group (52.2% vs. 27.3%, p=.217). However, a significant correlation between the time required for reperfusion and clinical outcome was detected, and this will serve as the rationale for encouraging a direct aspiration first pass technique as a first-line strategy in the acute vertebra-basilar artery. CONCLUSIONS: The a direct aspiration first pass technique first-line strategy for mechanical thrombectomy in posterior circulation may achieve successful recanalization with fewer attempts and shorter durations than the stent retriever first-line strategy.

Carotid artery stenting assisted with intravascular ultrasonography for isolated spontaneous common carotid artery dissection.

Isolated spontaneous common carotid artery (CCA) dissection is extremely rare. Moreover, only a few case reports for isolated spontaneous CCA dissection treated with carotid artery stenting (CAS) can be found so far. Here, the authors report a case where intravascular ultrasonography (IVUS) provided valuable information about lesion evaluation, stent selection and stent placement during CAS for isolated CCA dissection. A 69-year-old male was diagnosed with an isolated spontaneous left CCA dissection. CAS assisted with IVUS was performed to prevent further dissection and cerebral infarction recurrence. To the best of our knowledge, this is the first case report of an isolated spontaneous CCA dissection treated with CAS assisted by IVUS. CAS assisted by IVUS may be an effective treatment option to prevent intraoperative complications and further stroke recurrence for isolated spontaneous CCA dissection.

Plastid Anionic Lipids Are Essential for the Development of Both Photosynthetic and Non-Photosynthetic Organs in Arabidopsis thaliana.

The lipid bilayer matrix of the thylakoid membrane of cyanobacteria and chloroplasts of plants and algae is mainly composed of uncharged galactolipids, but also contains anionic lipids sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) as major constituents. The necessity of PG for photosynthesis is evident in all photosynthetic organisms examined to date, whereas the requirement of SQDG varies with species. In plants, although PG and SQDG are also found in non-photosynthetic plastids, their importance for the growth and functions of non-photosynthetic organs remains unclear. In addition, plants synthesize another anionic lipid glucuronosyldiacylglycerol (GlcADG) during phosphorus starvation, but its role in plant cells is not elucidated yet. To understand the functional relationships among PG, SQDG, and GlcADG, we characterized several Arabidopsis thaliana mutants defective in biosynthesis of these lipids. The mutants completely lacking both PG and SQDG biosynthesis in plastids showed developmental defects of roots, hypocotyls, and embryos in addition to leaves, which suggests that these lipids are pleiotropically required for the development of both photosynthetic and non-photosynthetic organs. Furthermore, our analysis revealed that SQDG, but not GlcADG, is essential for complementing the role of PG, particularly in photosynthesis under PG-deficient conditions such as phosphorus starvation.

The Leafless Orchid Cymbidium macrorhizon Performs Photosynthesis in the Pericarp during the Fruiting Season.

Photosynthesis with highly photoreactive chlorophyll (Chl) provides energy for plant growth but with simultaneous risk of photooxidative damage and photoprotection costs. Although the leafless orchid Cymbidium macrorhizon mostly depends on mycorrhizal fungi for carbon, it accumulates Chl particularly during fruiting and may not be fully mycoheterotrophic. In fact, stable isotopic analysis suggested that the fruiting C. macrorhizon specimens obtain a significant proportion of its carbon demands through photosynthesis. However, actual photosynthetic characteristics of this leafless orchid are unknown. To reveal the functionality of photosynthetic electron transport in C. macrorhizon, we compared its photosynthetic properties with those of its relative mixotrophic orchid Cymbidium goeringii and the model plant Arabidopsis thaliana. Compared with C. goeringii and A. thaliana, maximum photochemical efficiency of PSII was substantially low in C. macrorhizon. Chl fluorescence induction kinetics revealed that the electron transport capacity of PSII was limited in C. macrorhizon. Chl fluorescence analysis at 77 K suggested partial energetic disconnection of the light-harvesting antenna from the PSII reaction center in C. macrorhizon. Despite its low PSII photochemical efficiency, C. macrorhizon showed photosynthetic electron transport activity both in the field and under laboratory conditions. Cymbidium macrorhizon developed strong nonphotochemical quenching in response to increased light intensity as did C. goeringii, suggesting the functionality of photoprotective systems in this orchid. Moreover, C. macrorhizon fruit developed stomata on the pericarp and showed net O2-evolving activity. Our data demonstrate that C. macrorhizon can perform photosynthetic electron transport in the pericarp, although its contribution to net carbon acquisition may be limited.

Membrane lipid remodeling is required for photosystem II function under low CO2.

Membrane lipid remodeling in plants and microalgae has a crucial role in their survival under nutrient-deficient conditions. Aquatic microalgae have low access to CO2 , an essential carbon source for photosynthetic assimilates; however, 70-90 mol% of their membrane lipids are sugar-derived lipids (glycolipids) such as monogalactosyldiacylglycerol (MGDG). In this study, we discovered a new system of membrane lipid remodeling responding to CO2 in Synechocystis sp. PCC 6803, a unicellular, freshwater cyanobacterium. As compared with higher CO2 (HC; 1% CO2 ), under ambient air (lower CO2 : LC), phosphatidylglycerol (PG) content was increased at the expense of MGDG content. To explore the biological significance of this alteration in content, we generated a transformant of Synechocystis sp. PCC 6803 overexpressing sll0545 gene encoding a putative phosphatidic acid phosphate (oxPAP), which produces diacylglycerol that is used for the synthesis of glycolipids, and examined the effect on membrane lipid remodeling and phototrophic growth responding to LC. Photosystem II (PSII) activity and growth rate were inhibited under LC in oxPAP cells. PG content was substantially reduced, and MGDG and sulfoquinovosyldiacylglycerol contents were increased in oxPAP cells as compared with control cells. These phenotypes in oxPAP cells were recovered under the HC condition or PG supplementation. Increased PG content may be required for proper functioning of PSII under LC conditions.

A START domain-containing protein is involved in the incorporation of ER-derived fatty acids into chloroplast glycolipids in Marchantia polymorpha.

The appropriate regulation of thylakoid lipid synthesis is essential for the function of chloroplasts. In plant cells, membrane lipids synthesized in the ER are utilized as a precursor for the synthesis of chloroplast glycolipids. This pathway is thought to be mediated by the transport of glycerolipids synthesized in the ER into chloroplasts. However, we have little knowledge about the proteins involved in the lipid transfer between these organelles in plant cells. Here we show a protein, STAR2, containing the START (Steroidogenic acute regulatory protein-related lipid transfer) domain known to function as a lipid transporter, is involved in the incorporation of ER-derived fatty acids into chloroplast glycolipids in Marchantia polymorpha. We found that STAR2 localizes on the chloroplast envelope membrane as a punctuate structure and is required for the increase of C20 fatty acids, which are synthesized in the ER, in chloroplast glycolipids in response to phosphate deprivation. Our results indicate that STAR2 of M. polymorpha is likely to be involved in the lipid transfer from ER to chloroplast, presumably as a lipid transporter.

Long-Chain Saturated Fatty Acids, Palmitic and Stearic Acids, Enhance the Repair of Photosystem II.

Free fatty acids (FFA) generated in cyanobacterial cells can be utilized for the biodiesel that is required for our sustainable future. The combination of FFA and strong light induces severe photoinhibition of photosystem II (PSII), which suppresses the production of FFA in cyanobacterial cells. In the present study, we examined the effects of exogenously added FFA on the photoinhibition of PSII in Synechocystis sp. PCC 6803. The addition of lauric acid (12:0) to cells accelerated the photoinhibition of PSII by inhibiting the repair of PSII and the de novo synthesis of D1. α-Linolenic acid (18:3) affected both the repair of and photodamage to PSII. Surprisingly, palmitic (16:0) and stearic acids (18:0) enhanced the repair of PSII by accelerating the de novo synthesis of D1 with the mitigation of the photoinhibition of PSII. Our results show chemical potential of FFA in the regulation of PSII without genetic manipulation.

Role of Galactolipids in Plastid Differentiation Before and After Light Exposure.

Galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), are the predominant lipid classes in the thylakoid membrane of chloroplasts. These lipids are also major constituents of internal membrane structures called prolamellar bodies (PLBs) and prothylakoids (PTs) in etioplasts, which develop in the cotyledon cells of dark-grown angiosperms. Analysis of Arabidopsis mutants defective in the major galactolipid biosynthesis pathway revealed that MGDG and DGDG are similarly and, in part, differently required for membrane-associated processes such as the organization of PLBs and PTs and the formation of pigment-protein complexes in etioplasts. After light exposure, PLBs and PTs in etioplasts are transformed into the thylakoid membrane, resulting in chloroplast biogenesis. During the etioplast-to-chloroplast differentiation, galactolipids facilitate thylakoid membrane biogenesis from PLBs and PTs and play crucial roles in chlorophyll biosynthesis and accumulation of light-harvesting proteins. These recent findings shed light on the roles of galactolipids as key facilitators of several membrane-associated processes during the development of the internal membrane systems in plant plastids.