A diRNA-protein scaffold module mediates SMC5/6 recruitment in plant DNA repair.

In eukaryotes, the STRUCTURAL MAINTENANCE OF CHROMOSOME 5/6 (SMC5/6) complex is critical to maintaining chromosomal structures around double-strand breaks (DSBs) in DNA damage repair. However, the recruitment mechanism of this conserved complex at DSBs remains unclear. In this study, using Arabidopsis thaliana as a model, we found that SMC5/6 localization at DSBs is dependent on the protein scaffold containing INVOLVED IN DE NOVO 2 (IDN2), CELL DIVISION CYCLE 5 (CDC5), and ALTERATION/DEFICIENCY IN ACTIVATION 2B (ADA2b), whose recruitment is further mediated by DNA-damage-induced RNAs (diRNAs) generated from DNA regions around DSBs. The physical interactions of protein components including SMC5-ADA2b, ADA2b-CDC5, and CDC5-IDN2 result in formation of the protein scaffold. Further analysis indicated that the DSB localization of IDN2 requires its RNA-binding activity and ARGONAUTE 2 (AGO2), indicating a role for the AGO2-diRNA complex in this process. Given that most of the components in the scaffold are conserved, the mechanism presented here, which connects SMC5/6 recruitment and small RNAs, will improve our understanding of DNA repair mechanisms in eukaryotes.

Why can Mikania micrantha cover trees quickly during invasion?

The invasion of Mikania micrantha by climbing and covering trees has rapidly caused the death of many shrubs and trees, seriously endangering forest biodiversity. In this study, M. micrantha seedlings were planted together with local tree species (Cryptocarya concinna) to simulate the process of M. micrantha climbing under the forest. We found that the upper part of the M. micrantha stem lost its support after climbing to the top of the tree, grew in a turning and creeping manner, and then grew branches rapidly to cover the tree canopy. Then, we simulated the branching process through turning treatment. We found that a large number of branches had been formed near the turning part of the M. micrantha stem (TP). Compared with the upper part of the main stem (UP), the contents of plant hormones (auxin, cytokinin, gibberellin), soluble sugars (sucrose, glucose, fructose) and trehalose-6-phosphate (T6P) were significantly accumulated at TP. Further combining the transcriptome data of different parts of the main stem under erect or turning treatment, a hypothetical regulation model to illustrate how M. micrantha can quickly cover trees was proposed based on the regulation of sugars and hormones on plant branching; that is, the lack of support after ascending the top of the tree led to turning growth of the main stem, and the enhancement of sugars and T6P levels in the TP may first drive the release of nearby dormant buds. Plant hormone accumulation may regulate the entrance of buds into sustained growth and maintain the elongation of branches together with sugars to successfully covering trees.

Adaptation of the Invasive Plant Sphagneticola trilobata to Flooding Stress by Hybridization with Native Relatives.

Hybridization is common between invasive and native species and may produce more adaptive hybrids. The hybrid (Sphagneticola × guangdongensis) of Sphagneticola trilobata (an invasive species) and S. calendulacea (a native species) was found in South China. In this study, S. trilobata, S. calendulacea, and Sphagneticola × guangdongensis were used as research materials to explore their adaptability to flooding stress. Under flooding stress, the ethylene content and the expression of key enzyme genes related to ethylene synthesis in Sphagneticola × guangdongensis and S. calendulacea were significantly higher than those in S. trilobata. A large number of adventitious roots and aerenchyma were generated in Sphagneticola × guangdongensis and S. calendulacea. The contents of reactive oxygen species and malondialdehyde in Sphagneticola × guangdongensis and S. calendulacea were lower than those in S. trilobata, and the leaves of S. trilobata were the most severely damaged under flooding stress. The results indicate that hybridization catalyzed the tolerance of Sphagneticola × guangdongensis to flooding stress, and the responses of Sphagneticola × guangdongensis to flooding stress were more similar to that of its native parent. This suggests that hybridization with native relatives is an important way for invasive species to overcome environmental pressure and achieve invasion.

A SWI/SNF subunit regulates chromosomal dissociation of structural maintenance complex 5 during DNA repair in plant cells.

DNA damage decreases genome stability and alters genetic information in all organisms. Conserved protein complexes have been evolved for DNA repair in eukaryotes, such as the structural maintenance complex 5/6 (SMC5/6), a chromosomal ATPase involved in DNA double-strand break (DSB) repair. Several factors have been identified for recruitment of SMC5/6 to DSBs, but this complex is also associated with chromosomes under normal conditions; how SMC5/6 dissociates from its original location and moves to DSB sites is completely unknown. In this study, we determined that SWI3B, a subunit of the SWI/SNF complex, is an SMC5-interacting protein in Arabidopsis thialiana Knockdown of SWI3B or SMC5 results in increased DNA damage accumulation. During DNA damage, SWI3B expression is induced, but the SWI3B protein is not localized at DSBs. Notably, either knockdown or overexpression of SWI3B disrupts the DSB recruitment of SMC5 in response to DNA damage. Overexpression of a cotranscriptional activator ADA2b rescues the DSB localization of SMC5 dramatically in the SWI3B-overexpressing cells but only weakly in the SWI3B knockdown cells. Biochemical data confirmed that ADA2b attenuates the interaction between SWI3B and SMC5 and that SWI3B promotes the dissociation of SMC5 from chromosomes. In addition, overexpression of SMC5 reduces DNA damage accumulation in the SWI3B knockdown plants. Collectively, these results indicate that the presence of an appropriate level of SWI3B enhances dissociation of SMC5 from chromosomes for its further recruitment at DSBs during DNA damage in plant cells.

Photoprotection Differences between Dominant Tree Species at Mid- and Late-Successional Stages in Subtropical Forests in Different Seasonal Environments.

Plants growing in subtropical regions are often affected by high temperature and high light in summer and low temperature and high light in winter. However, few studies have compared the photoprotection mechanism of tree species at different successional stages in these two environments, although such studies would be helpful in understanding the succession of forest communities in subtropical forests. In order to explore the strategies used by dominant species at different successional stages to cope with these two environmental conditions, we selected two dominant species in the mid-successional stage, Schima superba and Castanopsis chinensis, and two dominant species in the late-successional stage, Machilus chinensis and Cryptocarya chinensis. The cell membrane permeability, chlorophyll fluorescence, chlorophyll content, and a few light-protective substances of these dominant species were measured in summer and winter. The results show that in summer, the young leaves of dominant species in the mid-successional stage showed higher anthocyanin content and superoxide dismutase (SOD) activity, while those in the late-successional stage showed higher flavonoid and total phenolic content, total antioxidant activity, non-photochemical quenching (NPQ), and carotenoid/chlorophyll (Car/Chl) ratio. In winter, young leaves of dominant species in the mid-successional stage were superior to those in the late-successional stage only in terms of catalase (CAT) activity and NPQ, while the anthocyanin, flavonoids, and total phenol content, total antioxidant capacity, and Car/Chl ratio were significantly lower compared to the late-successional stage. Our results show that the dominant species in different successional stages adapted to environmental changes in different seasons through the alterations in their photoprotection strategies. In summer, the dominant species in the mid-successional stage mainly achieved photoprotection through light shielding and reactive-oxygen-species scavenging by SOD, while the antioxidant capacity of trees in the late-successional stage mainly came from an increased antioxidative compounds and heat dissipation. In winter, the dominant species in the mid-successional stage maintained their photoprotective ability mainly through the scavenging of reactive oxygen species by CAT and the heat dissipation provided by NPQ, while those in the late-successional stage were mainly protected by a combination of processes, including light shielding, heat dissipation, and antioxidant effects provided by enzymatic and non-enzymatic antioxidant systems. In conclusion, our study partially explains the mechanism of community succession in subtropical forests.

Genome-Wide Characterization of PIN Auxin Efflux Carrier Gene Family in Mikania micrantha.

Mikania micrantha, recognized as one of the world's top 10 pernicious weeds, is a rapidly spreading tropical vine that has invaded the coastal areas of South China, causing serious economic losses and environmental damage. Rapid stem growth is an important feature of M. micrantha which may be related to its greater number of genes involved in auxin signaling and transport pathways and its ability to synthesize more auxin under adverse conditions to promote or maintain stem growth. Plant growth and development is closely connected to the regulation of endogenous hormones, especially the polar transport and asymmetric distribution of auxin. The PIN-FORMED (PIN) auxin efflux carrier gene family plays a key role in the polar transport of auxin and then regulates the growth of different plant tissues, which could indicate that the rapid growth of M. micrantha is closely related to this PIN-dependent auxin regulation. In this study, 11 PIN genes were identified and the phylogenetic relationship and structural compositions of the gene family in M. micrantha were analyzed by employing multiple bioinformatic methods. The phylogenetic analysis indicated that the PIN proteins could be divided into five distinct clades. The structural analysis revealed that three putative types of PIN (canonical, noncanonical and semi-canonical) exist among the proteins according to the length and the composition of the hydrophilic domain. The majority of the PINs were involved in the process of axillary bud differentiation and stem response under abiotic stress, indicating that M. micrantha may regulate its growth, development and stress response by regulating PIN expression in the axillary bud and stem, which may help explain its strong growth ability and environmental adaptability. Our study emphasized the structural features and stress response patterns of the PIN gene family and provided useful insights for further study into the molecular mechanism of auxin-regulated growth and control in M. micrantha.

Soil nitrogen dynamics and competition during plant invasion: insights from Mikania micrantha invasions in China.

Invasive plants often change a/biotic soil conditions to increase their competitiveness. We compared the microbially mediated soil nitrogen (N) cycle of invasive Mikania micrantha and two co-occurring native competitors, Persicaria chinensis and Paederia scandens. We assessed how differences in plant tissue N content, soil nutrients, N cycling rates, microbial biomass and activity, and diversity and abundance of N-cycling microbes associated with these species impact their competitiveness. Mikania micrantha outcompeted both native species by transferring more N to plant tissue (37.9-55.8% more than natives). We found total soil N to be at lowest, and available N highest, in M. micrantha rhizospheres, suggesting higher N cycling rates compared with both natives. Higher microbial biomass and enzyme activities in M. micrantha rhizospheres confirmed this, being positively correlated with soil N mineralization rates and available N. Mikania micrantha rhizospheres harbored highly diverse N-cycling microbes, including N-fixing, ammonia-oxidizing and denitrifying bacteria and ammonia-oxidizing archaea (AOA). Structural equation models indicated that M. micrantha obtained available N via AOA-mediated nitrification mainly. Field data mirrored our experimental findings. Nitrogen availability is elevated under M. micrantha invasion through enrichment of microbes that participate in N cycling, in turn increasing available N for plant growth, facilitating high interspecific competition.

The relationship between anthocyanin accumulation and photoprotection in young leaves of two dominant tree species in subtropical forests in different seasons.

Increasing amounts of experimental evidence show that anthocyanins provide physiological protection to plants under stress. However, the difference in photoprotection mediated by anthocyanins and other photoprotective substances in different seasons is still uncertain. To determine the relationship between anthocyanin accumulation and the photoprotective effects in different seasons, Castanopsis chinensis and Acmena acuminatissima, whose anthocyanin accumulation patterns differ in different seasons, were used as materials to explain how plants adapt to different seasons; as such, their physiological and biochemical responses were analyzed. Young leaves of C. chinensis and A. acuminatissima presented different colors in the different seasons. In summer, the young leaves of C. chinensis were purplish red, while those of A. acuminatissima were light green. In winter, the young leaves of C. chinensis were light green, while those of A. acuminatissima were red. Compared with the young red leaves, the young light green leaves that did not accumulate anthocyanins had higher flavonoid and phenolics contents, total antioxidant capacity, non-photochemical quenching (NPQ), and relative membrane leakage, and a slower recovery rate in the maximum photochemical efficiency (Fv/Fm) after high-light treatment. In addition, the net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (gs), and the effective quantum yield of PSII (ΦPSII) of the young leaves in winter were significantly lower than those in summer, while the activities of catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), and superoxide dismutase (SOD, EC 1.15.1.1) were significantly higher than those in summer. These data indicate that to adapt to seasonal changes anthocyanins, other antioxidative substances and antioxidative enzymes, as well as components involved in the safe dissipation of excitation energy as heat need to cooperate with one another.

The major photoprotective role of anthocyanins in leaves of Arabidopsis thaliana under long-term high light treatment: antioxidant or light attenuator?

Anthocyanins are water-soluble pigments in plants known for their photoprotective role against photoinhibitory and photooxidative damage under high light (HL). However, it remains unclear whether light-shielding or antioxidant activity plays a major role in the photoprotection exerted by anthocyanins under HL stress. To shed light on this question, we analyzed the physiological and biochemical responses to HL of three Arabidopsis thaliana lines (Col, chi, ans) with different light absorption and antioxidant characteristics. Under HL, ans had the highest antioxidant capacity, followed by Col, and finally chi; Col had the strongest light attenuation capacity, followed by chi, and finally ans. The line ans had weaker physiological activity of chloroplasts and more severe oxidative damage than chi after HL treatment. Col with highest photoprotection of light absorption capacity had highest resistance to HL among the three lines. The line ans with high antioxidant capacity could not compensate for its disadvantages in HL caused by the absence of the light-shielding function of anthocyanins. In addition, the expression level of the Anthocyanin Synthase (ANS) gene was most upregulated after HL treatment, suggesting that the conversion of colorless into colored anthocyanin precursors was necessary under HL. The contribution of anthocyanins to flavonoids, phenols, and antioxidant capacity increased in the late period of HL, suggesting that plants prefer to synthesize red anthocyanins (a group of colored antioxidants) over other colorless antioxidants to cope with HL. These experimental observations indicate that the light attenuation role of anthocyanins is more important than their antioxidant role in photoprotection.

Photosynthetic compensation of non-leaf organ stems of the invasive species Sphagneticola trilobata (L.) Pruski at low temperature.

Biological invasion is a hot topic in ecological research. Most studies on the physiological mechanisms of plants focus on leaves, but few studies focus on stems. To study the tolerance of invasive plant (Sphagneticola trilobata L.) to low temperature, relevant physiological indicators (including anthocyanin and chlorophyll) in different organs (leaves and stems) were analyzed, using a native species (Sphagneticola calendulacea L.) as the control. The results showed that, upon exposure to low temperature for 15 days, the stems of two Sphagneticola species were markedly reddened, their anthocyanin content increased, chlorophyll and chlorophyll fluorescence parameters decreased, and the accumulation of reactive oxygen species in the stem increased. The percentage increases of antioxidants and total antioxidant capacities in stems were significantly higher in S. trilobata than in S. calendulacea. This showed that S. trilobata had higher cold tolerance in stems while leaves were opposite. To further verify the higher cold tolerance of the stem of S. trilobata, a defoliation experiment was designed. We found that the defoliated stem of S. trilobata reduced anthocyanin accumulation and increased chlorophyll content, while alleviating membrane lipid damage and electrical conductivity, and the defoliated stem still showed an increase in stem diameter and biomass under low temperature. The discovery of the physiological and adaptive mechanisms of the stem of S. trilobata to low temperature will provide a theoretical basis for explaining how S. trilobata maintains its annual growth in South China. This is of great significance for predicting the future spread of cloned and propagated invasive plants.

Responses of Sphagneticola trilobata, Sphagneticola calendulacea and Their Hybrid to Drought Stress.

Sphagneticola trilobata is an invasive plant in South China. A hybrid between S. trilobata and Sphagneticola calendulacea (a native related species) has also been found in South China. The drought resistance of S. calendulacea, S. trilobata and their hybrid was studied in this paper. Under drought stress, the leaves of S. trilobata synthesized more abscisic acid (ABA) than those of the other species to reduce stomatal opening and water loss. The activities of antioxidant enzymes were the highest in S. trilobata and the lowest in S. calendulacea. The leaves of S. calendulacea suffered the most serious damage, and their maximum photochemical efficiency was the lowest. RNA-sequencing ware used to analyze the expression levels of genes in ABA, antioxidant enzyme, sugar and proline synthesis and photosynthesis pathways. Further real-time PCR detection verified the RNA-sequence results, and the results were in accordance with the physiological data. The results showed that S. trilobata was the most drought tolerant, and the drought tolerance of the hybrid did not show heterosis but was higher than S. calendulacea. Therefore, compared with S. trilobata and the hybrid, the population number and distribution of S. calendulacea may be less in arid areas.

Why Is the Invasive Plant Sphagneticola trilobata More Resistant to High Temperature than Its Native Congener?

Climate change and invasive alien species threaten biodiversity. High temperature is a worrying ecological factor. Most responses of invasive plants aimed at coping with adversity are focused on the physiological level. To explore the molecular mechanisms underlying the response of an invasive plant (Sphagneticola trilobata L.) to high temperature, using a native species (Sphagneticola calendulacea L.) as the control, relevant indicators, including photosynthetic pigments, gas exchange, chlorophyll fluorescence, the antioxidant system, and related enzyme-coding genes were measured. The results showed that the leaves of S. calendulacea turned yellow, photosynthetic pigment content (Chl a, Chl b, Car, Chl) decreased, gas exchange (Pn) and chlorophyll fluorescence parameters (Fv/Fm, ΦPSII) decreased under high temperature. It was also found that high temperature caused photoinhibition and a large amount of ROS accumulated, resulting in an increase in MDA and relative conductivity. Antioxidant enzymes (including SOD, POD, CAT, and APX) and antioxidants (including flavonoids, total phenols, and carotenoids) were decreased. The qPCR results further showed that the expression of the PsbP, PsbA, and RubiscoL, SOD, POD, CAT, and APX genes was downregulated, which was consistent with the results of physiological data. Otherwise, the resistance of S. trilobata to high temperature was better than that of S. calendulacea, which made it a superior plant in the invasion area. These results further indicated that the gradual warming of global temperature will greatly accelerate the invasion area of S. trilobata.

The effect of Funneliformis mosseae on the plant growth, Cd translocation and accumulation in the new Cd-hyperaccumulator Sphagneticola calendulacea.

The screening and identification of hyperaccumulators is the key to the phytoremediation of soils contaminated by heavy metal (HM). Arbuscular mycorrhizal fungus (AMF) can improve plant growth and tolerance to HM; therefore, AMF-assisted phytoextraction has been regarded as a potential technique for the remediation of HM-polluted soils. A greenhouse pot experiment was conducted to determine whether Sphagneticola calendulacea is a Cd-hyperaccumulator and to investigate the effect of the AMF-Funneliformis mosseae (FM) on plant growth and on the accumulation, subcellular distribution and chemical form of Cd in S. calendulacea grown in soils supplemented with different Cd levels. At 25, 50 and 100 mg Cd kg-1 level, S. calendulacea showed high Cd tolerance, the translocation factor and the bioconcentration factor exceeded 1, and accumulation of more than 100 mg Cd kg-1 was observed in the aboveground parts of the plant, meeting the requirements for a Cd-hyperaccumulator. Moreover, FM colonization significantly increased both biomasses and Cd concentration in S. calendulacea. After FM inoculation, the Cd concentrations and proportions increased in the cell walls, but exhibited no significant change in the organelles of the shoots. Meanwhile, FM symbiosis contributed to the conversion of Cd from highly toxic chemical forms (extracted by 80% ethanol and deionized water) to less toxic chemical forms (extracted by 1 M NaCl, 2% acetic acid, 0.6 M HCl) of Cd in the shoots. Overall, S. calendulacea is a typical Cd-hyperaccumulator, and FM symbiosis relieved the phytotoxicity of Cd and promoted plant growth and Cd accumulation, and thus greatly increasing the efficiency of phytoextraction for Cd-polluted soil. Our study provides a theoretical basis and application guidance for the remediation of Cd-contaminated soil by the symbiont of S. calendulacea with FM.

Arbuscular mycorrhizal fungi alleviate Cd phytotoxicity by altering Cd subcellular distribution and chemical forms in Zea mays.

Arbuscular mycorrhizal fungus (AMF) can relieve Cd phytotoxicity and improve plant growth, but the mechanisms involved in this process have still been not completely known. In the present work, a pot experiment was conducted to examine productions of glutathione (GSH) and phytochelatins (PCs), and absorption, chemical forms and subcellular distribution of Cd in maize (Zea mays) inoculated with or without AMF (Rhizophagus intraradices (Ri) and Glomus versiforme (Gv)) in Cd-amended soils (0, 1 and 5 mg Cd kg-1 soil). In general, both Ri and Gv inoculation dramatically enhanced biomass production and reduced Cd concentrations in shoots and roots of maize when compared to the non-mycorrhizal treatment. Moreover, both Ri and Gv symbiosis obviously increased contents of GSH and PCs, both in shoots and roots. Subcellular distribution of Cd in maize indicated that most of Cd (more than 90%) was accumulated in cell wall and soluble fraction. In addition, Cd proportions in soluble fractions in shoots of maize inoculated with Gv or Ri were considerably increased, but reduced in cell wall fractions compared to non-mycorrhizal maize, indicating that mycorrhizal symbiosis promoted Cd transfer to vacuoles. Furthermore, proportions of Cd in inorganic and water-soluble forms were declined, but elevated in pectates and proteins-integrated forms in mycorrhizal maize, which suggested that Gv and Ri could convert Cd into inactive forms. These observations could provide a further understanding of potential Cd detoxification mechanism in maize inoculated with AMF.

Phytotoxic effects of Cu, Cd and Zn on the seagrass Thalassia hemprichii and metal accumulation in plants growing in Xincun Bay, Hainan, China.

Seagrasses play an important role in coastal marine ecosystems, but they have been increasingly threatened by human activities. In recent years, seagrass communities have rapidly degenerated in the coastal marine ecosystems of China. To identify the reasons for the decline in seagrasses, the phytotoxic effects of trace metals (Cu, Cd and Zn) on the seagrass Thalassia hemprichii were investigated, and the environmental contents of the metals were analyzed where the seagrass grows. The results showed that leaf necrosis in T. hemprichii exposed to 0.01-0.1 mg L-1 of Cu2+ for 5 days was more serious than that in plants exposed to the same concentrations of Cd2+ and Zn2+. The chlorophyll content in T. hemprichii declined in a concentration-dependent manner after 5 days of exposure to Cu2+, Cd2+ and Zn2+. The evident reduction in ΔF/Fm' in T. hemprichii leaves was observed at day 1 of exposure to 0.01-1.0 mg L-1 of Cu2+ and at day 3 of exposure to 0.1-1.0 mg L-1 of Cd2+. The antioxidant enzyme activities (SOD, POD and CAT) in T. hemprichii leaves exposed to the three metal ions also showed significant changes. In seawater from Xincun Bay (Hainan, China), where T. hemprichii grows, Cu had reached a concentration (i.e., 0.01 mg L-1) that could significantly reduce chlorophyll content and ΔF/Fm' in T. hemprichii leaves. Our results indicate that Cu influences the deterioration of seagrasses in Xincun Bay.

Effects of a Dissostichus mawsoni-CaM recombinant proteins feed additive on the juvenile orange-spotted grouper (Epinephelus coioides) under the acute low temperature challenge.

The effects of Dissostichus mawsoni-Calmodulin (Dm-CaM) on growth performance, enzyme activities, respiratory burst, MDA level and immune-related gene expressions of the orange-spotted grouper (Epinephelus coioides) exposed to the acute low temperature stress were evaluated. The commercial diet supplemented with Dm-CaM protein was fed to the groupers for 6 weeks. No significant difference was observed in the specific growth rates, weight gains and survivals. After the feeding trial, the groupers were exposed to acute low temperature challenge. The groupers fed with Dm-CaM additive diet showed a significant decrease in the respiratory burst activity, while the blood cell number increased significantly at 25 °C by comparing with the control and additive control group. The enzymatic activity of SOD, ACP and ALP increased significantly in Dm-CaM additive group, while MDA level maintained stable with the lowest value. qRT-PCR analysis indicated that the up-regulated transcript expressions of CaM, C3, SOD2, LysC and HSPA4 were observed in Dm-CaM additive group. These results indicated that Dm-CaM additive diet may regulate the grouper immune response to the acute low temperature challenge.

Gibberellin indirectly promotes chloroplast biogenesis as a means to maintain the chloroplast population of expanded cells.

Chloroplast biogenesis needs to be well coordinated with cell division and cell expansion during plant growth and development to achieve optimal photosynthesis rates. Previous studies showed that gibberellins (GAs) regulate many important plant developmental processes, including cell division and cell expansion. However, the relationship between chloroplast biogenesis with cell division and cell expansion, and how GA coordinately regulates these processes, remains poorly understood. In this study, we showed that chloroplast division was significantly reduced in the GA-deficient mutants of Arabidopsis (ga1-3) and Oryza sativa (d18-AD), accompanied by the reduced expression of several chloroplast division-related genes. However, the chloroplasts of both mutants exhibited increased grana stacking compared with their respective wild-type plants, suggesting that there might be a compensation mechanism linking chloroplast division and grana stacking. A time-course analysis showed that cell expansion-related genes tended to be upregulated earlier and more significantly than the genes related to chloroplast division and cell division in GA-treated ga1-3 leaves, suggesting the possibility that GA may promote chloroplast division indirectly through impacting leaf mesophyll cell expansion. Furthermore, our cellular and molecular analysis of the GA-response signaling mutants suggest that RGA and GAI are the major repressors regulating GA-induced chloroplast division, but other DELLA proteins (RGL1, RGL2 and RGL3) also play a role in repressing chloroplast division in Arabidopsis. Taken together, our data show that GA plays a critical role in controlling and coordinating cell division, cell expansion and chloroplast biogenesis through influencing the DELLA protein family in both dicot and monocot plant species.

Thermal adaptation of photosynthetic physiology of the invasive vine Ipomoea cairica (L.) enhances its advantage over native Paederia scandens (Lour.) Merr. in South China.

Ipomoea cairica (L.) Sweet is an invasive vine in South China with strong ecological adaptability in tropical and subtropical ecosystems. However, its invasion mechanism under global warming still remains unknown. In the present study, the thermal adaptability of I. cairica was investigated from the perspective of photosynthetic physiology to explain its successful invasiveness in South China, compared to a niche-overlapping native vine Paederia scandens (Lour.) Merr. Results of field photosynthesis measurements indicated a higher photosynthesis of I. cairica than P. scandens, which was also more temperature-sensitive. Under heat treatment (40 °C), the thermal-avoidance strategy of P. scandens and the thermal-adaptation strategy of the I. cairica enhanced the photosynthetic growth advantage of I. cairica over P. scandens. In I. cairica, the increase of soluble sugar and antioxidant enzyme activity along with the decrease of Malondialdehyde and oxide accumulation demonstrated that I. cairica has superior thermal-adaptation, contrary to P. scandens. Expression of IcOr and IcSRO1 in I. cairica was induced at 40 °C, maintaining the stability of photosynthetic system II and enhancing antioxidant ability. Out study suggested that a higher frequency of heat disturbance under global warming will enhance the invasion capability I. cairica but inhibit the native vine P. scandens. HIGHLIGHT: This paper reveals that contrary thermal-adaptation strategies expanded the photosynthetic, growing, and physiological advantages of invasive I. cairica over native P. scandens under high temperature.

Dynamic changes of the contents of photoprotective substances and photosynthetic maturation during leaf development of evergreen tree species in subtropical forests.

Many studies have investigated the photoprotective and photosynthetic capacity of plant leaves, but few have simultaneously evaluated the dynamic changes of photoprotective capacity and photosynthetic maturation of leaves at different developmental stages. As a result, the process between the decline of photoprotective substances and the onset of photosynthetic maturation during plant leaf development are still poorly understood, and the relationship between them has not been quantitatively described. In this study, the contents of photoprotective substances, photosynthetic pigment content and photosynthetic capacity of leaves at different developmental stages from young leaves to mature leaves were determined by spatio-temporal replacement in eight dominant tree species in subtropical evergreen broadleaved forests. The correlation analysis found that the data sets of anthocyanins, flavonoids, total phenolics and total antioxidant capacity were mainly distributed on one side of the symmetry axis (y = x), while the data sets of flavonoids, total phenolics and total antioxidant capacity were mainly distributed on both sides of the symmetry axis (y = x). In addition, the content of photoprotective substances in plant leaves was significantly negatively correlated with photosynthetic pigment content and photosynthetic capacity but was significantly positively correlated with dark respiration rate (Rd). When chlorophyll accumulated to ~50% of the final value, the photoprotective substance content and Rd of plant leaves reached the lowest level, and anthocyanins disappeared completely; in contrast, the photosynthetic capacity reached the highest level. Our results suggest that anthocyanins mainly play a light-shielding role in the young leaves of most plants in subtropical forests. In addition, 50% chlorophyll accumulation in most plant leaves was the basis for judging leaf photosynthetic maturity. We also believe that 50% chlorophyll accumulation is a critical period in the transition of plant leaves from high photoprotective capacity (high metabolic capacity, low photosynthetic capacity) to low photoprotective capacity (low metabolic capacity, high photosynthetic capacity).

Adaptation of the Invasive Plant (Sphagneticola trilobata L. Pruski) to a High Cadmium Environment by Hybridizing With Native Relatives.

Invasive species can evolve rapidly in the invasion areas to adapt to new habitats. Sphagneticola trilobata L. Pruski, an invasive species, was studied for its tolerance to cadmium (Cd) in the soil and compared with its natural hybrid. From the perspective of photosynthetic physiology, antioxidant characteristics, and leaf hormone levels, the differences between the leaves of the two species before and after Cd treatment were compared. The results showed that the hybrid had stronger tolerance to Cd stress than invasive species. After Cd stress, the indexes of gas-exchange [net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), and transpiration rate (Tr)] of the hybrid was higher than invasive species, while the content of non-enzymatic antioxidants (flavonoids and total phenols) and antioxidant enzyme activities [peroxidase (POD) and superoxide dismutase (SOD)] was lower in hybrid than in invasive species. The changes in the content of plant hormones [auxin (IAA) and abscisic acid (ABA)] under Cd stress showed that hybrid can still maintain growth and prevent leaf senescence. Furthermore, the differences in gene expression between hybrid and invasive species in photosynthetic physiology, the antioxidant capacity of leaves, and endogenous hormone (IAA and ABA) synthesis pathway also showed that hybrid has stronger Cd tolerance than invasive species. This suggests that invasive species will realize the invasion through hybridization with the native relatives to overcome the stress from environmental factors. The study implied that hybridization between invasive species and native relatives is an important way for invasive species to spread in a wider and new environment that invasive species have not experienced in the area of origin.