Antenna Complexes Research Articles

Exogenous IAA improves the seedling growth of Syringa villosa via regulating the endogenous hormones and enhancing the photosynthesis

Auxin is a core regulator of plant growth and an effective promoter of cell division and cell expansion. Effects of auxin on improving plant growth of Syringa plants remain poorly elucidated. The present study was carried out to investigate the effects of exogenous indole-3-acetic acid (IAA) on morphogenesis, endogenous hormone content, photosynthesis capacity and find the basis of IAA-induced physiological effects of Syringa villosa by transcriptome sequencing technology. The results indicated that exogenous IAA significantly contributed to the plant height, stem diameter, leaf area and leaf number, which improved the accumulation of whole plant quality. Contents of endogenous IAA and gibberellic acid (GA3) were markedly higher than control after IAA treatment, while abscisic acid (ABA) content was significantly declined. For photosynthetic parameters, photosynthesis capacity was promoted by the application of IAA, as evidenced by a significant increase in net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) and a lower intercellular CO2 concentration (Ci). In addition, the transcriptome of S. villosa was first sequenced which revealed that genes related to the synthesis and signal transduction of growth-promoting hormones such as IAA, GA3, cytokinin (CTK), and brassinolide (BR) were significantly up-regulated within 2 h of IAA treatment. The expression levels of genes related to photosynthesis, antenna proteins, and carbon fixation of photosynthetic organisms were also enhanced by exogenous IAA. Additionally, the application of exogenous IAA had a positive effect on growth and development by rapidly inducing genes related to cell division and cell expansion. By profiling the transcriptome of IAA response, potential target genes were identified based on the hormone levels and photosynthesis. These results provide insights for further functional genomic studies on the regulatory mechanisms of IAA underlying Syringa plants architecture.

Molecular asymmetry of a photosynthetic supercomplex from green sulfur bacteria

The photochemical reaction center (RC) features a dimeric architecture for charge separation across the membrane. In green sulfur bacteria (GSB), the trimeric Fenna-Matthews-Olson (FMO) complex mediates the transfer of light energy from the chlorosome antenna complex to the RC. Here we determine the structure of the photosynthetic supercomplex from the GSB Chlorobaculum tepidum using single-particle cryogenic electron microscopy (cryo-EM) and identify the cytochrome c subunit (PscC), two accessory protein subunits (PscE and PscF), a second FMO trimeric complex, and a linker pigment between FMO and the RC core. The protein subunits that are assembled with the symmetric RC core generate an asymmetric photosynthetic supercomplex. One linker bacteriochlorophyll (BChl) is located in one of the two FMO-PscA interfaces, leading to differential efficiencies of the two energy transfer branches. The two FMO trimeric complexes establish two different binding interfaces with the RC cytoplasmic surface, driven by the associated accessory subunits. This structure of the GSB photosynthetic supercomplex provides mechanistic insight into the light excitation energy transfer routes and a possible evolutionary transition intermediate of the bacterial photosynthetic supercomplex from the primitive homodimeric RC.

Quadrupole Antenna and Diagnostic Complex for Ion Cyclotron Plasma Heating and Current Drive at the L-2M Stellarator

—A quadrupole antenna has been designed and produced at the L-2M stellarator for experiments on ion cyclotron plasma heating and current drive. Using a power meter of the incident and reflected waves, the first measurements of the radiation resistance of the antenna have been performed in the ohmic heating regime. The radiation resistance of the antenna has been measured as a function of the mean plasma density. It is shown that the fraction of absorbed power ensured by the coaxial modes is 25%. The created quadrupole antenna can also be used for current drive. The proposed method is based on the conversion of fast magnetosonic waves to slow magnetosonic waves with their subsequent absorption by plasma electrons, which is accompanied by current drive processes.

"Conical" Frustum Multi-Beam Phased Arrays for Air Traffic Control Radars.

The design of conical frustum phased array antennas for air traffic control (ATC) radar systems is addressed. The array architecture, which is controlled by a fully digital beam-forming (DBF) network, is composed by a set of equal vertical modules. Each module consists of a linear sparse array that generates on receive multiple instantaneous beams pointing along different directions in elevation. To reach the best trade-off between the antenna complexity (i.e., minimum number of array elements and/or radio frequency components) and radiation performance (i.e., matching a set of reference patterns), the synthesis problem is formulated in the Compressive Sampling (CS) framework. Then, the positions of the array elements and the complex excitations for generating each single beam are jointly determined through a customized version of the Bayesian CS (BCS) tool. Representative numerical results, concerned with ideal as well as real antenna models, are reported both to validate the proposed design strategy and to assess the effectiveness of the synthesized modular sparse array architecture also in comparison with conventional arrays with uniformly-spaced elements.

The major trimeric antenna complexes serve as a site for qH-energy dissipation in plants

Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants' survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state. Interestingly, we found that chlorophyll (Chl) fluorescence lifetimes were decreased by qH in isolated major trimeric antenna complexes, indicating that they serve as a site for qH-energy dissipation and providing a natively quenched complex with physiological relevance to natural conditions. Next, we monitored the changes in thylakoid pigment, protein, and lipid contents of antenna with active or inactive qH but did not detect any evident differences. Finally, we investigated whether specific subunits of the major antenna complexes were required for qH but found that qH was insensitive to trimer composition. Because we previously observed that qH can occur in the absence of specific xanthophylls, and no evident changes in pigments, proteins, or lipids were detected, we tentatively propose that the energy-dissipative state reported here may stem from Chl-Chl excitonic interaction.

AlphaFold and Structural Mass Spectrometry Enable Interrogations on the Intrinsically Disordered Regions in Cyanobacterial Light-harvesting Complex Phycobilisome

Intrinsically disordered proteins/regions (IDPRs) are a very large and functionally important class of proteins that participate in weak multivalent interactions in protein complexes. They are recalcitrant for interrogations using X-ray crystallography and cryo-EM. The IDPRs observed at the interface of the photosynthetic pigment protein complexes (PPCs) remain much less clear, e.g., the major cyanobacterial light-harvesting complex (PBS) contains an unstructured PB-loop insertion in the phycocyanobilin domain (PB domain) of ApcE (the largest polypeptide in PBS). Here, a joint platform is built to probe such structural domains. This platform is characterized by two-round progressive justifications of in silico models by using the structural mass spectrometry data. First, the AlphaFold-generated 3D structure of the PB domain (containing PB-loop) was justified in the context of PBS. Second, docking the AlphaFold-generated ApcG (a ligand) into the first-step justified structure (a receptor). The final ligand-receptor complex was then subjected to a second-round justification, again, by using unequivocal isotopically-encoded cross-links identified in LC-MS/MS. This work reveals a full-length PB-loop structure modelled in the PBS basal cylinder, free from any spatial conflicts against the other subunits in PBS. The structure of PB domain highlights the close associations of the intrinsically disordered PB-loop with its binding partners in PBS, including ApcG, another IDPR. The PB-loop region involved in the binding of photosystem II (PSII) is also discussed in the context of excitation energy transfer regulation. This work calls attention to the highly disordered, yet interrogatable interface between the light-harvesting antenna complexes and the reaction centers.

Transcriptome Analysis of the Responses of Rice Leaves to Chilling and Subsequent Recovery.

Improving chilling tolerance at the seedling stage in rice is essential for agricultural research. We combined a physiological analysis with transcriptomics in a variety Dular subjected to chilling followed by recovery at normal temperature to better understand the chilling tolerance mechanisms of rice. Chilling inhibited the synthesis of chlorophyll and non-structural carbohydrate (NSC) and disrupted the ion balance of the plant, resulting in the impaired function of rice leaves. The recovery treatment can effectively reverse the chilling-related injury. Transcriptome results displayed that 21,970 genes were identified at three different temperatures, and 11,732 genes were differentially expressed. According to KEGG analysis, functional categories for differentially expressed genes (DEGs) mainly included ribosome (8.72%), photosynthesis–antenna proteins (7.38%), phenylpropanoid biosynthesis (11.41%), and linoleic acid metabolism (10.07%). The subcellular localization demonstrated that most proteins were located in the chloroplasts (29.30%), cytosol (10.19%), and nucleus (10.19%). We proposed that some genes involved in photosynthesis, ribosome, phenylpropanoid biosynthesis, and linoleic acid metabolism may play key roles in enhancing rice adaptation to chilling stress and their recovery capacity. These findings provide a foundation for future research into rice chilling tolerance mechanisms.

Photocurrent generation following long-range propagation of organic exciton–polaritons

Natural photosynthesis exploited by both plants and bacteria provides essential energy and chemicals for sustaining life. A photosynthetic system often comprises antenna complexes (ACs) that absorb incident sunlight and deliver the molecular excited state energy to a central reaction center (RC) that converts the energy to charge. Numerous efforts have been made to mimic natural photosynthesis using organic materials. However, short-range energy transport due to material disorder has hindered their success. Here, we demonstrate a photodetector that mimics this natural architecture. It employs an AC that exploits exceptionally long-range ( ∼ 100 µ m ) Bloch surface wave polariton propagation that directs the excited states to an organic heterojunction detector serving as the RC. Exciton–polaritons are largely immune to localization due to the partial photonic character of the polariton, which consequently transports energy over extraordinary distances from its point of origin. Exciton–polaritons are edge-coupled into an RC that harvests excitation energy by dissociation into an electron and hole. This device relies on polariton-to-charge conversion combined with long-range energy transport for the direct detection of excited states in organic semiconductors. Our work paves the way for the realization of large-scale artificial photosynthetic systems comprising integrated organic photonic and optoelectronic devices with efficient energy transport and harvesting under ambient conditions.

Coplanar Meta-Surface-Based Substrate-Integrated Waveguide Antennas with Broadband and Low Reflections for K-Band Beam Scanning.

Four novel substrate-integrated waveguide (SIW) antennas are proposed, in order to obtain K-band beam scanning through the coplanar meta-surfaces of properly devised complementary split-ring resonators. More specifically, coplanar rhombus- and hexagon-shaped meta-surfaces replace the metallized via holes in the traditional SIW structure, achieving low reflection and wide bandwidth, respectively. Another trapezoid-shaped meta-surface is introduced, in order to realize good leaky-wave radiation performance with high-gain beam scanning in both rhombus- and hexagon-shaped SIW components. These designs are further extended to two different mixed types of two-row meta-surfaces, with the rhombus and hexagon structures combined in different orders to enhance the complex SIW transmission lines and antennas, which can simultaneously obtain good reflection and bandwidth with different priority, depending on the arrangement. We explain the performance differences with rhombus and hexagon meta-surfaces through the analysis of relevant equivalent circuit models and extracting the effective medium parameters, and we verify the bandwidths and radiations of four SIW antennas both numerically and experimentally. The maximum gains of the four antennas are 18.1 dBi, 17.0 dBi, 18.8 dBi and 17.1 dBi, where the corresponding relative bandwidths are 10.74%, 19.42%, 14.13% and 18.38%. The maximum simulated radiation efficiency and aperture efficiency of the proposed antennas are 91.20% and 61.12%, respectively. Our approach for generating flexible and selectable tuned electromagnetic fields from SIWs is applicable for the development of mm-Wave antennas or sensors on PCB-integrated platforms for highly directive scanning radiation.

Plasmon enhanced fluorescence of photosynthetic complexes by conjugating with gold micro-plates and their single-particle sensing application

Fundamental investigating and understanding the light harvesting process of natural antenna complexes will inspire and encourage us for rational design more efficient artificial devices for applications. Here, gold micro-plates are covalently linked with photosynthetic complexes, and their linked sites can be varied through adjusting the concentration of photosynthetic complexes. Significantly strong fluorescent emission enhancement has been observed from single gold micro-plate. When excited at 480 nm, the intensity enhancement is over two times higher than that excited at 405 nm, as the peridinin-chlorophyll-protein complexes prefer to absorbing light at 480 nm and they possess different pathways of energy transfer at different excitation wavelength. The synergistic effect originated from gold microplates make the enhancement factor of single peridinin-chlorophyll-protein complex from single gold micro-plate reach to 3.68 × 107, which could be utilized in designing single particle fluorescent sensor such as detecting Hg2+. Our method not only provides an effective way for significantly enhancing the fluorescent emission intensity and efficiency of light-harvesting, but also presents a robust single-particle application.

Spruce versus Arabidopsis: different strategies of photosynthetic acclimation to light intensity change.

The acclimation of higher plants to different light intensities is associated with a reorganization of the photosynthetic apparatus. These modifications, namely, changes in the amount of peripheral antenna (LHCII) of photosystem (PS) II and changes in PSII/PSI stoichiometry, typically lead to an altered chlorophyll (Chl) a/b ratio. However, our previous studies show that in spruce, this ratio is not affected by changes in growth light intensity. The evolutionary loss of PSII antenna proteins LHCB3 and LHCB6 in the Pinaceae family is another indication that the light acclimation strategy in spruce could be different. Here we show that, unlike Arabidopsis, spruce does not modify its PSII/PSI ratio and PSII antenna size to maximize its photosynthetic performance during light acclimation. Its large PSII antenna consists of many weakly bound LHCIIs, which form effective quenching centers, even at relatively low light. This, together with sensitive photosynthetic control on the level of cytochrome b6f complex (protecting PSI), is the crucial photoprotective mechanism in spruce. High-light acclimation of spruce involves the disruption of PSII macro-organization, reduction of the amount of both PSII and PSI core complexes, synthesis of stress proteins that bind released Chls, and formation of "locked-in" quenching centers from uncoupled LHCIIs. Such response has been previously observed in the evergreen angiosperm Monstera deliciosa exposed to high light. We suggest that, in contrast to annuals, shade-tolerant evergreen land plants have their own strategy to cope with light intensity changes and the hallmark of this strategy is a stable Chl a/b ratio.

Constant modulus shaped beam synthesis via linear fractional semidefinite relaxation

Excitation amplitude control is a critical issue regarding the shaped beam synthesis of array antennas. Ideally, excitations can have the same amplitude, and the desired beam can be achieved only by changing the phases. This method is called constant modulus synthesis, which can reduce the complexity of array antennas and is more conducive to the feeding, but it is really difficult to realize. In this paper, the authors derive a novel constant modulus beam synthesis algorithm, which uses the linear fractional semidefinite relaxation to relax the constant modulus constraints. Simulation results show that this method is stable and can maintain the excitation modulus while realizing the shaped beam.

Conformation of Light-Harvesting Complex II Trimer Depends upon Its Binding Site.

The light-harvesting complex II (LHCII) trimer in plants functions as a major antenna complex and a quencher to protect it from photooxidative damage. Theoretical studies on the structure of an LHCII trimer have demonstrated that excitation energy transfer between chlorophylls (Chls) in LHCII can be modulated by its exquisite conformational fluctuation. However, conformational changes depending on its binding location have not yet been investigated, even though reorganization of protein complexes occurs by physiological regulations. In this study, we investigated conformational differences in LHCII by comparing published structures of an identical LHCII trimer in the three different photosystem supercomplexes from the green alga Chlamydomonas reinhardtii. Our results revealed distinct differences in Chl configurations as well as polypeptide conformations of the LHCII trimers depending on its binding location. We propose that these configurational differences readily modulate the function of LHCII and possibly lead to a change in excitation-energy flow over the photosynthetic supercomplex.

Efficient Yield Estimation of Multiband Patch Antennas Using NLPLS-Based PCE

For high-volume manufacturing, yield estimation is an important design step to determine the effects of uncertainties in the fabrication process. The tolerances associated with the fabrication process are applied to the statistically significant system parameters, and a Monte Carlo (MC) simulation is historically done to accurately estimate the yield. This process becomes computationally very expensive when the number of statistically significant system parameters are either too difficult to intuitively determine or are too high. A nonlinear partial-least-squares-based polynomial chaos expansion (NLPLSs-based PCE) is proposed as a solution for complex antenna yield analysis. NLPLS-based PCE effectively reduces the system dimensionality using NLPLS and simultaneously extracts the statistical information on the same sample set, that is, yield, using PCE. It is also possible to perform a global sensitivity analysis using NLPLS-based PCE surrogates, providing an additional advantage. This method is illustrated using an eight-variable single-frequency patch antenna, an eight-variable dual-band patch antenna, and a 37-variable diplexer requiring 30, 10, and 30 analysis points, respectively, to obtain converged yield estimates.

On the Feasibility of Wireless Energy Transfer Based on Low Complexity Antenna Selection and Passive IRS Beamforming

We elucidate feasibility of wireless energy transfer (WET) with the help of an intelligent reflecting surface (IRS). We consider a source equipped with multiple antennas and a single radio-frequency (RF) chain. We propose a low complexity rule that does joint antenna selection (AS) at source and passive beamforming at IRS. We derive new expressions for probability of outage in WET under perfect and estimated channel knowledge and for both single and multiple users. We derive intuitive expressions for outage probability with large number of IRS elements and for line-of-sight scenarios. For a system with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> antennas at source and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> passive elements at IRS, we show that diversity order equals <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M+N$ </tex-math></inline-formula> . Extensions to subset AS, discrete phase-shift design, and performance under limited scattering are also presented. Our numerical results show that the proposed AS rule yields near-optimal performance while requiring only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M+N$ </tex-math></inline-formula> pilot transmissions compared to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M+MN$ </tex-math></inline-formula> pilot transmissions required by the optimal AS rule in literature. We elucidate that we can trade-off active RF chains at source with passive elements at IRS to obtain improved performance both in terms of outage probability and power transfer efficiency. And 3-bit IRS is sufficient to obtain good performance at lower complexity.

Macromolecular conformational changes in photosystem II: interaction between structure and function.

Conformational changes play an important role in the functioning of proteins and their complexes. This is also true for the pigment-protein super-complex of photosystem II (PSII). The data testify about the pH-induced macromolecular conformational changes in the water-oxidizing complex (WOC) on the donor side of PSII, the interaction between the spatial structure of WOC proteins and the distribution of cytochrome b559 redox-forms, and the electron transfer efficiency between QA and QB on the acceptor side of PSII. Changes in the protein environment near QA and QB can be observed after the removal of the bicarbonate ion associated with non-heme Fe or after the addition of herbicides binding to the QB site, which results in the suppression of the electron transfer in this site. The "locking" of the de novo assembled PSII in an inactive state until WOC activation is also accompanied by strong structural perturbations on the PSII acceptor and donor sides with the participation of Psb28 and Psb27 proteins. The triggers for degradation and replacement of damaged PSII proteins are structural changes induced by their oxidative modification and aggregation. Macromolecular changes in the antenna proteins underlie the activation of photoprotective non-photochemical quenching, which are induced by protonation of the lumenal residues of PsbS or/and Lhcsr3, as well as the phosphorylation of antenna proteins. Besides this, many smaller-scale conformational changes may occur in PSII. This review summarizes current knowledge about the possible conformational changes in proteins in the PSII super-complex and describes their proposed influence on PSII function.

ФОТОХІМІЧНА АКТИВНІСТЬ ЛИСТКІВ СОЇ ЗА ДІЇ ФІТОПАТОГЕННИХ БАКТЕРІЙ РІЗНОЇ ВІРУЛЕНТНОСТІ

Soybean plants were grown in a greenhouse. In the phase of 4-6 leaves soybeans were artificially infected with strains of pathogens: Xanthomonas axonopodis pv. glycines 9284 and Xanthomonas axonopodis pv. phaseoli 8843. These strains were obtained from the Ukrainian collection of microorganisms of the Zabolotny institute of Microbiology and Virology of National Academy of Sciences of Ukraine. The photochemical activity of soybean leaves was determined by the biophysical method of chlorophyll fluorescence induction in 13 days after plant inoculation with bacterial strains. A portable Florotest fluorometer was use for measurements. A degree of chlorophyll degradation and suppression of photosynthetic activity in soybean leaves at artificial infection with bacterial strains isolated from different plant species of the Fabaceaeae family dependent from its virulence have been shown. The strain X. axonopodis pv. glycines 9284, isolated from soybean plants, have been highly virulent and acted more negatively than the low virulent to soybean strain X. axonopodis pv. phaseoli 8843. In particular, the value of the minimum fluorescence F0 decreased by 37.0 and 15.4 % for inoculation by strains with different virulence degree: X. axonopodis pv. glycines 9284 (from soybeans) and X. axonopodis pv. phaseoli 8843 (from beans) respectively. There was also a significant decrease in the value of Fm in these variants – by 54.9 % (X. axonopodis pv. glycines 9284) and 19.3 % (X. axonopodis pv. phaseoli 8843). At the same time, the value of maximum quantum yield of PSII (Fv / Fm) was decreased by 11.8 % in the variant with inoculation of soybean plants with the highly virulent strain X. axonopodis pv. glycines 9284, that indicates photoinhibition or damage of antenna complexes of the PSII photosynthetic apparatus of soybean plants. At the same time, only the tendency to reduce the maximum quantum yield of PSII was determined under action infection plants with X. axonopodis pv. phaseoli 8843. A parameter chlorophyll fluorescence decrease ratio Rfd, which shows the activity of CO2 assimilation in the Calvin cycle, was inhibition more at the action of artificial infection with a highly virulent strain – X. axonopodis pv. glycines 9284 – 54.5 and less – at infection with a low virulence strain – X. axonopodis pv. phaseoli 8843 – by 10.8 %. With prolonged action of the pathogenic bacterial strains X.axonopodis pv. glycines 9284 and the X. axonopodis pv. phaseoli 8843 (fortnight) showed significant inhibition of the catalase and peroxidase activity of leaf tissues, which is evidence of an increase in the formation of ROS. It was demonstrated that the highly virulent strain X.axonopodis pv. glycines 9284 most of all suppressed the catalase activity of soybean leaf tissues.

Transcriptome Approach Reveals the Response Mechanism of Heimia myrtifolia (Lythraceae, Myrtales) to Drought Stress.

Drought is a major environmental condition that inhibits the development and cultivation of Heimia myrtifolia. The molecular processes of drought resistance in H. myrtifolia remain unknown, which has limited its application. In our study, transcriptome analyzes were compared across three treatment groups (CK, T1, and T2), to investigate the molecular mechanism of drought resistance. Plant leaves wilted and drooped as the duration of drought stress increased. The relative water content of the leaves declined dramatically, and relative electrolyte leakage rose progressively. Using an RNA-Seq approach, a total of 62,015 unigenes with an average length of 1730 bp were found, with 86.61% of them annotated to seven databases, and 14,272 differentially expressed genes (DEGs) were identified in drought stress. GO and KEGG enrichment analyzes of the DEGs revealed significantly enriched KEGG pathways, including photosynthesis, photosynthetic antenna proteins, plant hormone signal transduction, glutathione metabolism, and ascorbate and aldarate metabolism. Abscisic acid signal transduction was the most prevalent in the plant hormone signal transduction pathway, and other plant hormone signal transductions were also involved in the drought stress response. The transcription factors (including MYB, NAC, WRKY, and bHLH) and related differential genes on significantly enriched pathways all played important roles in the drought process, such as photosynthesis-related genes and antioxidant enzyme genes. In conclusion, this study will provide several genetic resources for further investigation of the molecular processes that will be beneficial to H. myrtifolia cultivation and breeding.

Physiological and comparative transcriptome analysis of the response and adaptation mechanism of the photosynthetic function of mulberry (Morus alba L.) leaves to flooding stress

ABSTRACT Flooding has become one of the major abiotic stresses that seriously affects plant growth and development owing to changes in the global precipitation pattern. Mulberry (Morus alba L.) is a desirable tree spePhysocarpus amurensis Maxim andcies with high ecological and economic benefits. To reveal the response and adaptive mechanisms of the photosynthetic functions of mulberry leaves to flooding stress, chlorophyll synthesis, photosynthetic electron transfer and the Calvin cycle were investigated by physiological studies combined with an analysis of the transcriptome. Flooding stress inhibited the synthesis of chlorophyll (Chl) and decreased its content in mulberry leaves. The sensitivity of Chl a to flooding stress was higher than that of Chl b owing to the changes of CHLG (LOC21385082) and CAO (LOC21408165) that encode genes during chlorophyll synthesis. The levels of expression of Chl b reductase NYC (LOC112094996) and NYC (LOC21385774), which are involved in Chl b degradation, were upregulated on the fifteenth day of flooding, which accelerated the transformation of Chl b to Chl a, and upregulated the expression of PPH (LOC21385040) and PAO (LOC21395013). This accelerated the degradation of chlorophyll. Flooding stress significantly inhibited the photosynthetic function of mulberry leaves. A Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of differentially expressed genes under different days of flooding stress indicated significant enrichment in Photosynthesis-antenna proteins (map00196), Photosynthesis (map00195) and Carbon fixation in photosynthetic organisms (map00710). On the fifth day of flooding, 7 and 5 genes that encode antenna proteins were identified on LHCII and LHCI, respectively. They were significantly downregulated, and the degree of downregulation increased as the trees were flooded longer. Therefore, the power of the leaves to capture solar energy and transfer this energy to the reaction center was reduced. The chlorophyll fluorescence parameters and related changes in the expression of genes in the transcriptome indicated that the PSII and PSI of mulberry leaves were damaged, and their activities decreased under flooding stress. On the fifth day of flooding, electron transfer on the PSII acceptor side of mulberry leaves was blocked, and the oxygen-evolving complex (OEC) on the donor side was damaged. On the tenth day of flooding, the thylakoid membranes of mulberry leaves were damaged. Five of the six coding genes that mapped to the OEC were significantly downregulated. Simultaneously, other coding genes located at the PSII reaction center and those located at the PSI reaction center, including Cytb6/f, PC, Fd, FNR and ATP, were also significantly downregulated. In addition, the gas exchange parameters (P n, G s, T r, and C i) of the leaves decreased after 10 days of flooding stress primarily owing to the stomatal factor. However, on the fifteenth day of flooding, the value for the intracellular concentration of CO2 was significantly higher than that on the tenth day of flooding. In addition, the differentially expressed genes identified in the Calvin cycle were significantly downregulated, suggesting that in addition to stomatal factors, non-stomatal factors were also important factors that mediated the decrease in the photosynthetic capacity of mulberry leaves. In conclusion, the inhibition of growth of mulberry plants caused by flooding stress was primarily related to the inhibition of chlorophyll synthesis, antenna proteins, photosynthetic electron transfer and the Calvin cycle. The results of this study provide a theoretical basis for the response and mechanism of adaptation of the photosynthetic function of mulberry to flooding stress.

Fine-mapping and transcriptome analysis of the photosensitive leaf -yellowing gene CaLY1 in pepper (Capsicum annuum L.)

Leaf color is directly related to altered photosynthesis. Hence, leaf yellowing mutants can be widely used for the researching plant physiology and functional genomes, for cultivating new varieties of popular horticultural plants, and for identifying hybrid purity (as markers). Here, we constructed a 60Co-γ F2 population from the leaf -yellowing mutant R24 via radiation mutation with the inbred line WT21 of pepper. Genetic analysis showed that the leaf-yellowing of the mutant was controlled by a single recessive gene. By applying the Bulk Segregation Analysis and Kompetitive Allele Specific PCR markers, the leaf-yellowing gene CaLY1 (Capsicum annuum Leaf yellow 1) was mapped on chromosome 9, SNP5791587–SNP6011215, with a size of 214.5 kb. One non-synonymous mutated gene Capana09g000166 was found in the interval. The gene encoded a PsbX, which is the core complex of PSII. Transcriptome analysis further showed that 2301 differentially expressed genes were identified under shading treatment for 24 h in R24. The Gene Ontology enrichment pathways were related to photosynthesis light harvesting, cell wall, activity of quercetin 3-O-glucosyltransferase and flavonoid metabolic process, which likely regulate the response of pepper leaves to different light levels. Functional enrichment analysis indicated that the most abundant pathways were photosynthesis antenna proteins and metabolic.