Genome-Wide Identification of Pentatricopeptide Repeat (PPR) Gene Family and Multi-Omics Analysis Provide New Insights Into the Albinism Mechanism of Kandelia obovata Propagule Leaves.

Pentatricopeptide repeat (PPR) gene family constitutes one of the largest gene families in plants, which mainly participate in RNA editing and RNA splicing of organellar RNAs, thereby affecting the organellar development. Recently, some evidence elucidated the important roles of PPR proteins in the albino process of plant leaves. However, the functions of PPR genes in the woody mangrove species have not been investigated. In this study, using a typical true mangrove Kandelia obovata, we systematically identified 298 PPR genes and characterized their general features and physicochemical properties, including evolutionary relationships, the subcellular localization, PPR motif type, the number of introns and PPR motifs, and isoelectric point, and so forth. Furthermore, we combined genome-wide association studies (GWAS) and transcriptome analysis to identify the genetic architecture and potential PPR genes associated with propagule leaves colour variations of K. obovata. As a result, we prioritized 16 PPR genes related to the albino phenotype using different strategies, including differentially expressed genes analysis and genetic diversity analysis. Further analysis discovered two genes of interest, namely Maker00002998 (PLS-type) and Maker00003187 (P-type), which were differentially expressed genes and causal genes detected by GWAS analysis. Moreover, we successfully predicted downstream target chloroplast genes (rps14, rpoC1 and rpoC2) bound by Maker00002998 PPR proteins. The experimental verification of RNA editing sites of rps14, rpoC1, and rpoC2 in our previous study and the verification of interaction between Maker00002998 and rps14 transcript using in vitro RNA pull-down assays revealed that Maker00002998 PPR protein might be involved in the post-transcriptional process of chloroplast genes. Our result provides new insights into the roles of PPR genes in the albinism mechanism of K. obovata propagule leaves.

Combined metabolome and transcriptome analysis reveals a critical role of lignin biosynthesis and lignification in stem-like pneumatophore development of the mangrove Avicennia marina.

MAIN CONCLUSION: Transcriptional and metabolic regulation of lignin biosynthesis and lignification plays crucial roles in Avicennia marina pneumatophore development, facilitating its adaptation to coastal habitats. Avicennia marina is a pioneer mangrove species in coastal wetland. To cope with the periodic intertidal flooding and hypoxia environment, this species has developed a complex and extensive root system, with its most unique feature being a pneumatophore with a distinct above- and below-ground morphology and vascular structure. However, the characteristics of pneumatophore lignification remain unknown. Studies comparing the anatomy among above-ground pneumatophore, below-ground pneumatophore, and feeding root have suggested that vascular structure development in the pneumatophore is more like the development of a stem than of a root. Metabolome and transcriptome analysis illustrated that the accumulation of syringyl (S) and guaiacyl (G) units in the pneumatophore plays a critical role in lignification of the stem-like structure. Fourteen differentially accumulated metabolites (DAMs) and 10 differentially expressed genes involved in the lignin biosynthesis pathway were targeted. To identify genes significantly associated with lignification, we analyzed the correlation between 14 genes and 8 metabolites and further built a co-expression network between 10 transcription factors (TFs), including 5 for each of MYB and NAC, and 23 enzyme-coding genes involved in lignin biosynthesis. 4-Coumarate-CoA ligase, shikimate/quinate hydroxycinnamoyl transferase, cinnamyl alcohol dehydrogenase, caffeic acid 3-O-methyltransferase, phenylalanine ammonia-lyase, and peroxidase were identified to be strongly correlated with these TFs. Finally, we examined 9 key candidate genes through quantitative real-time PCR to validate the reliability of transcriptome data. Together, our metabolome and transcriptome findings reveal that lignin biosynthesis and lignification regulate pneumatophore development in the mangrove species A. marina and facilitate its adaptation to coastal habitats.

Hydrogen sulfide upregulates the alternative respiratory pathway in mangrove plant Avicennia marina to attenuate waterlogging-induced oxidative stress and mitochondrial damage in a calcium-dependent manner.

Hydrogen sulfide (H2 S) is considered to mediate plant growth and development. However, whether H2 S regulates the adaptation of mangrove plant to intertidal flooding habitats is not well understood. In this study, sodium hydrosulfide (NaHS) was used as an H2 S donor to investigate the effect of H2 S on the responses of mangrove plant Avicennia marina to waterlogging. The results showed that 24-h waterlogging increased reactive oxygen species (ROS) and cell death in roots. Excessive mitochondrial ROS accumulation is highly oxidative and leads to mitochondrial structural and functional damage. However, the application of NaHS counteracted the oxidative damage caused by waterlogging. The mitochondrial ROS production was reduced by H2 S through increasing the expressions of the alternative oxidase genes and increasing the proportion of alternative respiratory pathway in the total mitochondrial respiration. Secondly, H2 S enhanced the capacity of the antioxidant system. Meanwhile, H2 S induced Ca2+ influx and activated the expression of intracellular Ca2+ -sensing-related genes. In addition, the alleviating effect of H2 S on waterlogging can be reversed by Ca2+ chelator and Ca2+ channel blockers. In conclusion, this study provides the first evidence to explain the role of H2 S in waterlogging adaptation in mangrove plants from the mitochondrial aspect.

Comparative Proteomic Analysis Reveals the Regulatory Effects of H2S on Salt Tolerance of Mangrove Plant Kandelia obovata.

As a dominant mangrove species, Kandelia obovata is distributed in an intertidal marsh with an active H2S release. Whether H2S participates in the salt tolerance of mangrove plants is still ambiguous, although increasing evidence has demonstrated that H2S functions in plant responses to multiple abiotic stresses. In this study, NaHS was used as an H2S donor to investigate the regulatory mechanism of H2S on the salt tolerance of K. obovata seedlings by using a combined physiological and proteomic analysis. The results showed that the reduction in photosynthesis (Pn) caused by 400 mM of NaCl was recovered by the addition of NaHS (200 µM). Furthermore, the application of H2S enhanced the quantum efficiency of photosystem II (PSII) and the membrane lipid stability, implying that H2S is beneficial to the survival of K. obovata seedlings under high salinity. We further identified 37 differentially expressed proteins by proteomic approaches under salinity and NaHS treatments. Among them, the proteins that are related to photosynthesis, primary metabolism, stress response and hormone biosynthesis were primarily enriched. The physiological and proteomic results highlighted that exogenous H2S up-regulated photosynthesis and energy metabolism to help K. obovata to cope with high salinity. Specifically, H2S increased photosynthetic electron transfer, chlorophyll biosynthesis and carbon fixation in K. obovata leaves under salt stress. Furthermore, the abundances of other proteins related to the metabolic pathway, such as antioxidation (ascorbic acid peroxidase (APX), copper/zinc superoxide dismutase (CSD2), and pancreatic and duodenal homeobox 1 (PDX1)), protein synthesis (heat-shock protein (HSP), chaperonin family protein (Cpn) 20), nitrogen metabolism (glutamine synthetase 1 and 2 (GS2), GS1:1), glycolysis (phosphoglycerate kinase (PGK) and triosephosphate isomerase (TPI)), and the ascorbate-glutathione (AsA-GSH) cycle were increased by H2S under high salinity. These findings provide new insights into the roles of H2S in the adaptations of the K. obovata mangrove plant to high salinity environments.

Photonics meets topology.

The topological phases in materials have been studied in recent decades for their unique boundary states and transport properties. Photonic systems with band structures embrace the topological phases closely, where they not only provide platforms to testify the topological band theory, but also shed light on designing novel optical devices. In this review, we present exciting developments, supported by brief descriptions of prominent milestones of topological phases in photonic systems in recent years. These studies may sustain further developments of optical devices and offer novel methods for light manipulations.

Z2 topological edge state in honeycomb lattice of coupled resonant optical waveguides with a flat band.

Two-dimensional (2D) coupled resonant optical waveguide (CROW), exhibiting topological edge states, provides an efficient platform for designing integrated topological photonic devices. In this paper, we propose an experimentally feasible design of 2D honeycomb CROW photonic structure. The characteristic optical system possesses two-fold and three-fold Dirac points at different positions in the Brillouin zone. The effective gauge fields implemented by the intrinsic pseudo-spin-orbit interaction open up topologically nontrivial bandgaps through the Dirac points. Spatial lattice geometries allow destructive wave interference, leading to a dispersionless, near-flat energy band in the vicinity of the three-fold Dirac point in the telecommunication frequency regime. This nontrivial structure with a near-flat band yields topologically protected edge states. These characteristics underpin the fundamental importance as well as the potential applications in various optical devices. Based on the honeycomb CROW lattice, we design the shape-independent topological cavity and the beam splitter, which demonstrate the relevance for a wide range of photonic applications.

Structural, developmental and functional analyses of leaf salt glands of mangrove recretohalophyte Aegiceras corniculatum.

Salt secretion is an important strategy used by the mangrove plant Aegiceras corniculatum to adapt to the coastal intertidal environment. However, the structural, developmental and functional analyses on the leaf salt glands, particularly the salt secretion mechanism, are not well documented. In this study, we investigated the structural, developmental and degenerative characteristics and the salt secretion mechanisms of salt glands to further elucidate the mechanisms of salt tolerance of A. corniculatum. The results showed that the salt gland cells have a large number of mitochondria and vesicles, and plenty of plasmodesmata as well, while chloroplasts were found in the collecting cells. The salt glands developed early and began to differentiate at the leaf primordium stage. We observed and defined three stages of salt gland degradation for the first time in A. corniculatum, where the secretory cells gradually twisted and wrinkled inward and collapsed downward as the salt gland degeneration increased and the intensity of salt gland autofluorescence gradually diminished. In addition, we found that the salt secretion rate of the salt glands increased when the treated concentration of NaCl increased, reaching the maximum at 400 mM NaCl. The salt-secreting capacity of the salt glands of the adaxial epidermis is significantly greater than that of the abaxial epidermis. The real-time quantitative PCR results indicate that SAD2, TTG1, GL2 and RBR1 may be involved in regulating the development of the salt glands of A. corniculatum. Moreover, Na+/H+ antiporter, H+-ATPase, K+ channel and Cl- channel may play important roles in the salt secretion of salt glands. In sum mary, this study strengthens the understanding of the structural, developmental and degenerative patterns of salt glands and salt secretion mechanisms in mangrove recretohalophyte A. corniculatum, providing an important reference for further studies at the molecular level.

Integrative analysis of transcriptome and metabolome reveal the differential tolerance mechanisms to low and high salinity in the roots of facultative halophyte Avicennia marina.

Mangroves perform a crucial ecological role along the tropical and subtropical coastal intertidal zone where salinity fluctuation occurs frequently. However, the differential responses of mangrove plant at the combined transcriptome and metabolome level to variable salinity are not well documented. In this study, we used Avicennia marina (Forssk.) Vierh., a pioneer species of mangrove wetlands and one of the most salt-tolerant mangroves, to investigate the differential salt tolerance mechanisms under low and high salinity using inductively coupled plasma-mass spectrometry, transcriptomic and metabolomic analysis. The results showed that HAK8 was up-regulated and transported K+ into the roots under low salinity. However, under high salinity, AKT1 and NHX2 were strongly induced, which indicated the transport of K+ and Na+ compartmentalization to maintain ion homeostasis. In addition, A. marina tolerates low salinity by up-regulating ABA signaling pathway and accumulating more mannitol, unsaturated fatty acids, amino acids' and L-ascorbic acid in the roots. Under high salinity, A. marina undergoes a more drastic metabolic network rearrangement in the roots, such as more L-ascorbic acid and oxiglutatione were up-regulated, while carbohydrates, lipids and amino acids were down-regulated in the roots, and, finally, glycolysis and TCA cycle were promoted to provide more energy to improve salt tolerance. Our findings suggest that the major salt tolerance traits in A. marina can be attributed to complex regulatory and signaling mechanisms, and show significant differences between low and high salinity.

Calcium regulates the physiological and molecular responses of Morus alba roots to cadmium stress.

Heavy metal cadmium (Cd) is toxic to organisms. Mulberry (Morus alba L.) is a fast-growing perennial that is also an economical Cd phytoremediation material with large biomass. However, the molecular mechanisms underlying its Cd tolerance remain unclear. Here, we reveal the physiological and molecular mechanisms underlying Cd toxicity under varying calcium (Ca) treatments. First, under low-Ca treatment (0.1 mM Ca), mulberry growth was severely inhibited and the root surface structure was damaged by Cd stress. Second, electrophysiological data demonstrated that 0.1 mM Ca induced an increased Cd2+ influx, leading to its accumulation in the entire root and root cell walls. Third, high-Ca treatment (10 mM Ca) largely alleviated growth inhibition, activated antioxidant enzymes, increased Ca content, decreased Cd2+ flux, and inhibited Cd uptake by roots. Finally, 0.1 mM Ca resulted in the activation of metal transporters and the disruption of Ca signaling-related gene expression, which facilitated Cd accumulation in the roots, aggravating oxidative stress. These adverse effects were reversed by treatment with 10 mM Ca. This study preliminarily revealed the mechanism by which varying Ca levels regulate Cd uptake and accumulation in mulberry roots, provided an insight into the interrelationships between Ca and Cd in the ecological and economic tree mulberry and offered a theoretical basis for Ca application in managing Cd pollution.

Proteomic analysis reveals differential responsive mechanisms in Solanum nigrum exposed to low and high dose of cadmium.

Cadmium (Cd) contamination is becoming a widespread environmental problem. However, the differential responsive mechanisms of Cd hyperaccumulator Solanum nigrum to low or high dose of Cd are not well documented. In this study, phenotypic and physiological analysis firstly suggested that the seedlings of S. nigrum showed slight leaf chlorosis symptoms under 25 µM Cd and severe inhibition on growth and photosynthesis under 100 µM Cd. Further proteomic analysis identified 105 differentially expressed proteins (DEPs) in the Cd-treated leaves. Under low dose of Cd stress, 47 DEPs are mainly involved in primary metabolic processes, while under high dose of Cd stress, 92 DEPs are mainly involved in photosynthesis, energy metabolism, production of phytochelatin and reactive oxygen species (ROS). Protein-protein interaction (PPI) network analysis of DEPs support above differential responses in the leaves of S. nigrum to low and high dose of Cd treatments. This work provides the differential responsive mechanisms in S. nigrum to low and high dose of Cd, and the theoretical foundation for the application of hyperaccumulating plants in the phytoremediation of Cd-contaminated soils.

Leaf sodium homeostasis controlled by salt gland is associated with salt tolerance in mangrove plant Avicennia marina.

Avicennia marina, a mangrove plant growing in coastal wetland habitats, is frequently affected by tidal salinity. To understand its salinity tolerance, the seedlings of A. marina were treated with 0, 200, 400 and 600 mM NaCl. We found the whole-plant dry weight and photosynthetic parameters increased at 200 mM NaCl but decreased over 400 mM NaCl. The maximum quantum yield of primary photochemistry (Fv/Fm) significantly decreased at 600 mM NaCl. Transmission electron microscopy observations showed high salinity caused the reduction in starch grain size, swelling of the thylakoids and separation of the granal stacks, and even destruction of the envelope. In addition, the dense protoplasm and abundant mitochondria in the secretory and stalk cells, and abundant plasmodesmata between salt gland cells were observed in the salt glands of the adaxial epidermis. At all salinities, Na+ content was higher in leaves than in stems and roots; however, Na+ content increased in the roots while it remained at a constant level in the leaves over 400 mM NaCl treatment, due to salt secretion from the salt glands. As a result, salt crystals on the leaf adaxial surface increased with salinity. On the other hand, salt treatment increased Na+ and K+ efflux and decreased H+ efflux from the salt glands by the non-invasive micro-test technology, although Na+ efflux reached the maximum at 400 mM NaCl. Further real-time quantitative PCR analysis indicated that the expression of Na+/H+ antiporter (SOS1 and NHX1), H+-ATPase (AHA1 and VHA-c1) and K+ channel (AKT1, HAK5 and GORK) were up-regulated, and only the only Na+ inward transporter (HKT1) was down-regulated in the salt glands enriched adaxial epidermis of the leaves under 400 mM NaCl treatment. In conclusion, salinity below 200 mM NaCl was beneficial to the growth of A. marina, and below 400 mM, the salt glands could excrete Na+ effectively, thus improving its salt tolerance.

Inventory of cadmium-transporter genes in the root of mangrove plant Avicennia marina under cadmium stress.

Mangrove Avicennia marina has the importantly potential for cadmium (Cd) pollution remediation in coastal wetlands. Unfortunately, the molecular mechanisms and transporter members for Cd uptake by the roots of A. marina are not well documented. In this study, photosynthetic and phenotypic analysis indicated that A. marina is particularly tolerant to Cd. The content and flux analysis indicated that Cd is mainly retained in the roots, with greater Cd influx in fine roots than that in coarse roots, and higher Cd influx in the root meristem zone as well. Using transcriptomic analysis, a total of 5238 differentially expressed genes were identified between the Cd treatment and control group. Moreover, we found that 54 genes were responsible for inorganic ion transport. Among these genes, AmHMA2, AmIRT1, and AmPCR2 were localized in the plasma membrane and AmZIP1 was localized in both plasma membrane and cytoplasm. All above gene encoding transporters showed significant Cd transport activities using function assay in yeast cells. In addition, the overexpression of AmZIP1 or AmPCR2 in Arabidopsis improved the Cd tolerance of transgenic plants. This is particularly significant as it provides insight into the molecular mechanism for Cd uptake by the roots of mangrove plants and a theoretical basis for coastal wetland phytoremediation.

Cadmium promotes the absorption of ammonium in hyperaccumulator Solanum nigrum L. mediated by ammonium transporters and aquaporins.

Cadmium (Cd) is a toxic heavy metal affecting the normal growth of plants. Nitrate (NO3-) and ammonium (NH4+) are the primary forms of inorganic nitrogen (N) absorbed by plants. However, the mechanism of N absorption and regulation under Cd stress remains unclear. This study found that: (1) Cd treatment affected the biomass, root length, and Cd2+ flux in Solanum nigrum seedling roots. Specifically, 50 µM Cd significantly inhibited NO3- influx while increased NH4+ influx compared with 0 and 5 µM Cd treatments measured by non-invasive micro-test technology. (2) qRT-PCR analysis showed that 50 µM Cd inhibited the expressions of nitrate transporter genes, SnNRT2;4 and SnNRT2;4-like, increased the expressions of ammonium transporter genes, SnAMT1;2 and SnAMT1;3, in the roots. (3) Under NH4+ supply, 50 µM Cd significantly induced the expressions of the aquaporin genes, SnPIP1;5, SnPIP2;7, and SnTIP2;1. Our results showed that 50 µM Cd stress promoted NH4+ absorption by up-regulating the gene expressions of NH4+ transporter and aquaporins, suggesting that high Cd stress can affect the preference of N nutrition in S. nigrum.

Physiological and Proteomic Analyses of Different Ecotypes of Reed (Phragmites communis) in Adaption to Natural Drought and Salinity.

Drought and salinity are the two major abiotic stresses constraining the crop yield worldwide. Both of them trigger cellular dehydration and cause osmotic stress which leads to cytosolic and vacuolar volume reduction. However, whether plants share a similar tolerance mechanism in response to these two stresses under natural conditions has seldom been comparatively reported. There are three different ecotypes of reed within a 5 km2 region in the Badanjilin desert of Northwest China. Taking the typical swamp reed (SR) as a control, we performed a comparative study on the adaption mechanisms of the two terrestrial ecotypes: dune reed (DR) and heavy salt meadow reed (HSMR) by physiological and proteomic approaches coupled with bioinformatic analysis. The results showed that HSMR and DR have evolved C4-like photosynthetic and anatomical characteristics, such as the increased bundle sheath cells (BSCs) and chloroplasts in BSCs, higher density of veins, and lower density and aperture of stomata. In addition, the thylakoid membrane fluidity also plays an important role in their higher drought and salinity tolerance capability. The proteomic results further demonstrated that HSMR and DR facilitated the regulation of proteins associated with photosynthesis and energy metabolism, lipid metabolism, transcription and translation, and stress responses to well-adapt to the drought and salinity conditions. Overall, our results demonstrated that HSMR and DR shaped a similar adaption strategy from the structural and physiological levels to the molecular scale to ensure functionality in a harsh environment.

Parity-Time Symmetry in Non-Hermitian Complex Optical Media.

The exploration of quantum-inspired symmetries in optical and photonic systems has witnessed immense research interest both fundamentally and technologically in a wide range of subject areas in physics and engineering. One of the principal emerging fields in this context is non-Hermitian physics based on parity-time symmetry, originally proposed in the studies pertaining to quantum mechanics and quantum field theory and recently ramified into a diverse set of areas, particularly in optics and photonics. The intriguing physical effects enabled by non-Hermitian physics and PT symmetry have enhanced significant application prospects and engineering of novel materials. In addition, there has been increasing research interest in many emerging directions beyond optics and photonics. Here, the state-of-the art developments in the field of complex non-Hermitian physics based on PT symmetry in various physical settings are brought together, and key concepts, a background, and a detailed perspective on new emerging directions are described. It can be anticipated that this trendy field of interest will be indispensable in providing new perspectives in maneuvering the flow of light in the diverse physical platforms in optics, photonics, condensed matter, optoelectronics, and beyond, and will offer distinctive application prospects in novel functional materials.

Spartina alterniflora invasion alters soil bacterial communities and enhances soil N2O emissions by stimulating soil denitrification in mangrove wetland.

Chinese mangrove, an important ecosystem in coastal wetlands, is sensitive to the invasive alien species Spartina alterniflora. However, the effects of the S. alterniflora invasion on mangrove soil N2O emissions and the underlying mechanisms by which emissions are affected have not been well studied. In this study, the N2O emitted from soils dominated by two typical native mangroves (i.e. Kandelia obovata: KO; Avicennia marina: AM), one invaded by S. alterniflora (SA), and one bare mudflat (Mud) were monitored at Zhangjiang Mangrove Estuary (where S. alterniflora is exotic). Together with soil biogeochemical properties, the potential denitrification rate and the composition of soil bacterial communities were determined simultaneously by 15NO3- tracer and high-throughput sequencing techniques, respectively. Our results showed that S. alterniflora invasion significantly (p < 0.05) increases soil N2O emissions by 15-28-fold. In addition, isotope results revealed that the soil potential denitrification rate was significantly (p < 0.05) enhanced after S. alterniflora invasion. Moreover, the S. alterniflora invasion significantly (p < 0.05) decreased soil bacterial α-diversity and strongly modified soil bacterial communities. Indicator groups strongly associated with S. alterniflora were Chloroflexia, Alphaproteobacteria, and Bacilli, each of which was abundant and acts as connector in the co-occurrence network. FAPROTAX analysis implied that the S. alterniflora invasion stimulated soil denitrification and nitrification while depressing anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA). Redundancy analysis (RDA) found that soil organic matter (SOM) and pH were the most important environmental factors in altering soil bacterial communities. Taken together, our results imply that the S. alterniflora invasion in mangrove wetlands significantly stimulates soil denitrification and N2O emissions, thereby contributing N2O to the atmosphere and contributing to global climate change.

Elevated nitrogen metabolism and nitric oxide production are involved in Arabidopsis resistance to acid rain.

Acid rain (AR) can induce great damages to plants and could be classified into different types according to the different SO42-/NO3- ratio. However, the mechanism of plants' responding to different types of AR has not been elucidated clearly. Here, we found that nitric-rich simulated AR (N-SiAR) induced less leaves injury as lower necrosis percentage, better physiological parameters and reduced oxidative damage in the leaves of N-SiAR treated Arabidopsis thaliana compared with sulfate and nitrate mixed (SN-SiAR) or sulfuric-rich (S-SiAR) simulated AR treated ones. Of these three types of SiAR, N-SiAR treated Arabidopsis maintained the highest of nitrogen (N) content, nitrate reductase (NR) and nitrite reductase (NiR) activity as well as N metabolism related genes expression level. Nitric oxide (NO) content showed that N-SiAR treated seedlings had a higher NO level compared to SN-SiAR or S-SiAR treated ones. A series of NO production and elimination related reagents and three NO production-related mutants were used to further confirm the role of NO in regulating acid rain resistance in N-SiAR treated Arabidopsis seedlings. Taken together, we concluded that an elevated N metabolism and enhanced NO production are involved in the tolerance to different types of AR in Arabidopsis.

Exotic Spartina alterniflora invasion increases CH4 while reduces CO2 emissions from mangrove wetland soils in southeastern China.

Mangroves are critical in global carbon budget while vulnerable to exotic plant invasion. Spartina alterniflora, one of typical salt marsh plant grows forcefully along the coast of China, has invaded the native mangrove habitats in Zhangjiang Estuary. However, the effects of S. alterniflora invasion on soil carbon gases (CH4 and CO2) emission from mangroves are not fully understood. Accordingly, we conducted a field experiment to investigate the soil CH4 and CO2 emission during growing seasons in 2016 and 2017 at four adjacent wetlands, namely bare mudflat (Mud), Kandelia obovata (KO), Avicennia marina (AM) and S. alterniflora (SA). Potential methane production (PMP), potential methane oxidation (PMO), functional microbial abundance and soil biogeochemical properties were measured simultaneously. Our results indicate that S. alterniflora invasion could dramatically increase soil CH4 emissions mainly due to the enhancement in PMP which facilitated by soil EC, MBC, TOC and mcrA gene abundance. Additionally, S. alterniflora invasion decreases soil CO2 emission. Both heterotrophic microbial respiration (16S rRNA) and methane oxidation (pmoA and ANME-pmoA) are responsible for CO2 emission reduction. Furthermore, S. alterniflora invasion greatly increases GWP by stimulating CH4 emissions. Thus, comparing with mangroves, invasive S. alterniflora significantly (p < 0.001) increases CH4 emission while reduces CO2 emission.

Proteomic analysis on mangrove plant Avicennia marina leaves reveals nitric oxide enhances the salt tolerance by up-regulating photosynthetic and energy metabolic protein expression.

Avicennia marina (Forsk.) Vierh is one of the most salt-tolerant mangrove species. Our previous study revealed that nitric oxide (NO) enhanced the salt tolerance of A. marina by promoting salt secretion and Na+ sequestration under salt stress. However, little is known about the regulation of NO on proteomic profiling for this mangrove species. In this study, we used sodium nitroprusside (SNP), an NO donor, to investigate the regulatory mechanism of NO on salt tolerance of A. marina according to physiological and proteomic aspects. Photosynthesis data showed that the reduction in photosynthesis caused by high salinity treatment (400 mM NaCl) could be partially recovered by addition of SNP (100 µM). Further analysis revealed that the high salinity treatment could induce not only the stomatal limitation but also non-stomatal limitation on photosynthetic reduction, while SNP addition could restore the non-stomatal limitation, implying that the application of SNP was beneficial to the metabolic process in leaves. Proteomic analysis identified 49 differentially expressed proteins involved in various biological processes such as photosynthesis, energy metabolism, primary metabolism, RNA transcription, protein translation and stress response proteins. Under high salinity treatment, the abundances of proteins related to photosynthesis, such as ribulose-phosphate 3-epimerase (RPE, spot 3), RuBisCO large subunit (RBCL, spot 4, 5, 24), RuBisCO activase A (RCA, spot 17, 18) and quinine oxidoreductase-like protein isoform 1 (QOR1, spot 23), were significantly decreased. However, the abundance of proteins such as RBCL (spot 5, 9) and QOR1 (spot 23) were increased by SNP addition. In addition, exogenous NO supply alleviated salt tolerance by increasing the accumulation of some proteins involved in energy metabolism (spot 15), primary metabolism (spot 25, 45, 46), RNA transcription (spot 36) and stress response proteins (spot 12, 21, 26, 37, 43). The transcriptional levels of nine selected proteins were mostly consistent with their protein abundance except spot 46. Overall, the presented data demonstrated that NO has a positive effect on improving salt tolerance in A. marina by regulating the protein abundance involved in photosynthesis, energy metabolism, primary metabolism and stress response.

[An analysis of genetic diversity of different ecotypes of reed (Phragmites communis Trin.) by molecular marker techniques].

ISSR (inter-simple sequence repeat) and RAPD (random-amplified polymorphic DNA) markers were used to detect genetic diversity of 4 different ecotypes of reed (Phragmites communis Trin.) growing in Hexi Corridor, Gansu province. Nine effective primers were screened from 30 ISSR arbitrary primers, and a total of 99 DNA bands were amplified, among which 51 (51.5%) were polymorphic. Thirteen effective primers were screened from 45 RAPD 10-oligonucleotide arbitrary primers, and a total of 195 DNA bands were amplified, among which 87 (44.6%) were polymorphic. Genetic identity based on ISSR and RAPD data showed a positive correlation (r=0.845, P<0.05). Based on unweighted pair-group method with arithmetic averages (UPGMA) cluster analysis on DNA bands amplified, together with the correlation analysis between genetic distance and soil water contents and soluble salt contents as well, the present results suggest that the genetic diversity occurs among the four ecotypes of reed in adaptation to long term natural drought and salinity, showing an obvious evolutional tendency from swamp reed via salt meadow reed to dune reed.