Effects of nitrate- and ammonium- nitrogen on anatomical and physiological responses of Catalpa bungei under full and partial root-zone drought.

Catalpa bungei is a precious timber species distributed in North China where drought often occurs. To clarify adaptive responses of C. bungei to partial- and full- root-zone drought under the influence of nitrogen forms, a two-factor experiment was conducted in which well-watered (WW), partial root-zone drought in horizontal direction (H-PRD) and in vertical direction (V-PRD), and full root-zone drought (FRD) were combined with nitrate-nitrogen (NN) and ammonium-nitrogen (AN) treatments. C. bungei responded to FRD by sharply closing stomata, decreasing gas exchange rate and increasing leaf instantaneous water use efficiency (WUEi). Under FRD condition, the growth of seedlings was severely inhibited and the effect of N forms was covered up by the drastic drought effect. In comparison, stomata conductance and gas exchanges were moderately inhibited by PRDs. WUEi in V-PRD treatment was superior to H-PRD due to the active stomata regulation resulting from a higher ABA level and active transcription of genes in abscisic acid (ABA) signaling pathway under V-PRD. Under both PRDs and FRD, nitrate benefited antioxidant defense, stomata regulation and leaf WUEi. Under V-PRD, WUEi in nitrate treatment was superior to that in ammonium treatment due to active stomata regulation by signaling network of nitric oxide (NO), Ca2+ and ABA. Under FRD, WUEi was higher in nitrate treatment due to the favoring photosynthetic efficiency resulting from active NO signal and antioxidant defense. The interactive effect of water and N forms was significant on wood xylem development. Superoxide dismutase (SOD) and catalase (CAT) largely contributes to stress tolerance and xylem development.

Genome-Wide Identification and Expression Analysis of the SQUAMOSA Promoter-Binding Protein-like (SPL) Transcription Factor Family in Catalpabungei.

As a plant-specific transcription factor, the SPL gene family plays a critical role in plant growth and development. Although the SPL gene family has been identified in diverse plant species, there have been no genome-wide identification or systematic study reports on the SPL gene family in Catalpa bungei. In this study, we identified 19 putative SPL gene family members in the C. bungei genome. According to the phylogenetic relationship, they can be divided into eight groups, and the genes in the same group have a similar gene structure and conserved motifs. Synteny analysis showed that fragment duplication played an important role in the expansion of the CbuSPL gene family. At the same time, CbuSPL genes have cis-acting elements and functions related to light response, hormone response, growth and development, and stress response. Tissue-specific expression and developmental period-specific expression analysis showed that CbuSPL may be involved in flowering initiation and development, flowering transition, and leaf development. In addition, the ectopic expression of CbuSPL4 in Arabidopsis confirmed that it can promote early flowering and induce the expression of related flowering genes. These systematic research results will lay a foundation for further study on the functional analysis of SPL genes in C. bungei.

Genome-wide analysis of lncRNA and mRNA expression and endogenous hormone regulation during tension wood formation in Catalpa bungei.

BACKGROUND: Phytohormones are the key factors regulating vascular development in plants, and they are also involved in tension wood (TW) formation. Although the theory of hormone distribution in TW formation is widely supported, the effects of endogenous hormones on TW formation have not yet been assessed. In this study, TW formation was induced in Catalpa bungei by artificial bending. The phytohormone content of TW, opposite wood (OW) and normal wood (NW) was determined using liquid chromatography-mass spectrometry (LC-MS), and transcriptome sequencing was performed. The hormone content and related gene expression data were comprehensively analyzed. RESULTS: The results of analyses of the plant hormone contents indicated significantly higher levels of cis-zeatin (cZ), indoleacetic acid (IAA) and abscisic acid (ABA) in TW than in OW. Genes involved in the IAA and ABA synthesis pathways, such as ALDH (evm. MODEL: group5.1511) and UGT (evm. MODEL: scaffold36.20), were significantly upregulated in TW. and the expression levels of ARF (evm. MODEL: group5.1332), A-ARR (evm. MODEL: group0.1600), and TCH4 (evm. MODEL: group2.745), which participate in IAA, cZ and Brassinolide (BR) signal transduction, were significantly increased in TW. In particular, ARF expression may be regulated by long noncoding RNAs (lncRNAs) and the HD-ZIP transcription factor ATHB-15. CONCLUSIONS: We constructed a multiple hormone-mediated network of C. bungei TW formation based on hormone levels and transcriptional expression profiles were identified during TW formation.

Multi-omics sequencing provides insight into floral transition in Catalpa bungei. C.A. Mey.

BACKGROUND: Floral transition plays an important role in development, and proper time is necessary to improve the value of valuable ornamental trees. The molecular mechanisms of floral transition remain unknown in perennial woody plants. "Bairihua" is a type of C. bungei that can undergo floral transition in the first planting year. RESULTS: Here, we combined short-read next-generation sequencing (NGS) and single-molecule real-time (SMRT) sequencing to provide a more complete view of transcriptome regulation during floral transition in C. bungei. The circadian rhythm-plant pathway may be the critical pathway during floral transition in early flowering (EF) C. bungei, according to horizontal and vertical analysis in EF and normal flowering (NF) C. bungei. SBP and MIKC-MADS-box were seemingly involved in EF during floral transition. A total of 61 hub genes were associated with floral transition in the MEturquoise model with Weighted Gene Co-expression Network Analysis (WGCNA). The results reveal that ten hub genes had a close connection with the GASA homologue gene (Cbu.gene.18280), and the ten co-expressed genes belong to five flowering-related pathways. Furthermore, our study provides new insights into the complexity and regulation of alternative splicing (AS). The ratio or number of isoforms of some floral transition-related genes is different in different periods or in different sub-genomes. CONCLUSIONS: Our results will be a useful reference for the study of floral transition in other perennial woody plants. Further molecular investigations are needed to verify our sequencing data.

Potential function of CbuSPL and gene encoding its interacting protein during flowering in Catalpa bungei.

BACKGROUND: "Bairihua", a variety of the Catalpa bungei, has a large amount of flowers and a long flowering period which make it an excellent material for flowering researches in trees. SPL is one of the hub genes that regulate both flowering transition and development. RESULTS: SPL homologues CbuSPL9 was cloned using degenerate primers with RACE. Expression studies during flowering transition in "Bairihua" and ectopic expression in Arabidopsis showed that CbuSPL9 was functional similarly with its Arabidopsis homologues. In the next step, we used Y2H to identify the proteins that could interact with CbuSPL9. HMGA, an architectural transcriptional factor, was identified and cloned for further research. BiFC and BLI showed that CbuSPL9 could form a heterodimer with CbuHMGA in the nucleus. The expression analysis showed that CbuHMGA had a similar expression trend to that of CbuSPL9 during flowering in "Bairihua". Intriguingly, ectopic expression of CbuHMGA in Arabidopsis would lead to aberrant flowers, but did not effect flowering time. CONCLUSIONS: Our results implied a novel pathway that CbuSPL9 regulated flowering development, but not flowering transition, with the participation of CbuHMGA. Further investments need to be done to verify the details of this pathway.

Transcriptomics and Proteomics Reveal the Cellulose and Pectin Metabolic Processes in the Tension Wood (Non-G-Layer) of Catalpa bungei.

: Catalpa bungei is an economically important tree with high-quality wood and highly valuable to the study of wood formation. In this work, the xylem microstructure of C. bungei tension wood (TW) was observed, and we performed transcriptomics, proteomics and Raman spectroscopy of TW, opposite wood (OW) and normal wood (NW). The results showed that there was no obvious gelatinous layer (G-layer) in the TW of C. bungei and that the secondary wall deposition in the TW was reduced compared with that in the OW and NW. We found that most of the differentially expressed mRNAs and proteins were involved in carbohydrate polysaccharide synthesis. Raman spectroscopy results indicated that the cellulose and pectin content and pectin methylation in the TW were lower than those in the OW and NW, and many genes and proteins involved in the metabolic pathways of cellulose and pectin, such as galacturonosyltransferase (GAUT), polygalacturonase (PG), endoglucanase (CLE) and ß-glucosidase (BGLU) genes, were significantly upregulated in TW. In addition, we found that the MYB2 transcription factor may regulate the pectin degradation genes PG1 and PG3, and ARF, ERF, SBP and MYB1 may be the key transcription factors regulating the synthesis and decomposition of cellulose. In contrast to previous studies on TW with a G-layer, our results revealed a change in metabolism in TW without a G-layer, and we inferred that the change in the pectin type, esterification and cellulose characteristics in the TW of C. bungei may contribute to high tensile stress. These results will enrich the understanding of the mechanism of TW formation.

Construction of a high-density genetic map and QTL mapping of leaf traits and plant growth in an interspecific F1 population of Catalpa bungei × Catalpa duclouxii Dode.

BACKGROUND: Catalpa bungei is an important tree species used for timber in China and widely cultivated for economic and ornamental purposes. A high-density linkage map of C. bungei would be an efficient tool not only for identifying key quantitative trait loci (QTLs) that affect important traits, such as plant growth and leaf traits, but also for other genetic studies. RESULTS: Restriction site-associated DNA sequencing (RAD-seq) was used to identify molecular markers and construct a genetic map. Approximately 280.77 Gb of clean data were obtained after sequencing, and in total, 25,614,295 single nucleotide polymorphisms (SNPs) and 2,871,647 insertions-deletions (InDels) were initially identified in the genomes of 200 individuals of a C. bungei (7080) × Catalpa duclouxii (16-PJ-3) F1 population and their parents. Finally, 9072 SNP and 521 InDel markers that satisfied the requirements for constructing a genetic map were obtained. The integrated genetic map contained 9593 pleomorphic markers in 20 linkage groups and spanned 3151.63 cM, with an average distance between adjacent markers of 0.32 cM. Twenty QTLs for seven leaf traits and 13 QTLs for plant height at five successive time points were identified using our genetic map by inclusive composite interval mapping (ICIM). Q16-60 was identified as a QTL for five leaf traits, and three significant QTLs (Q9-1, Q18-66 and Q18-73) associated with plant growth were detected at least twice. Genome annotation suggested that a cyclin gene participates in leaf trait development, while the growth of C. bungei may be influenced by CDC48C and genes associated with phytohormone synthesis. CONCLUSIONS: This is the first genetic map constructed in C. bungei and will be a useful tool for further genetic study, molecular marker-assisted breeding and genome assembly.

Genome-wide analysis of long non-coding RNAs in Catalpa bungei and their potential function in floral transition using high-throughput sequencing.

BACKGROUND: Long non-coding RNAs (lncRNAs) have crucial roles in various biological regulatory processes. However, the study of lncRNAs is limited in woody plants. Catalpa bungei is a valuable ornamental tree with a long cultivation history in China, and a deeper understanding of the floral transition mechanism in C. bungei would be interesting from both economic and scientific perspectives. RESULTS: In this study, we categorized C. bungei buds from early flowering (EF) and normal flowering (NF) varieties into three consecutive developmental stages. These buds were used to systematically study lncRNAs during floral transition using high-throughput sequencing to identify molecular regulatory networks. Quantitative real-time PCR was performed to study RNA expression changes in different stages. In total, 12,532 lncRNAs and 26,936 messenger RNAs (mRNAs) were detected. Moreover, 680 differentially expressed genes and 817 differentially expressed lncRNAs were detected during the initiation of floral transition. The results highlight the mRNAs and lncRNAs that may be involved in floral transition, as well as the many lncRNAs serving as microRNA precursors. We predicted the functions of lncRNAs by analysing the relationships between lncRNAs and mRNAs. Seven lncRNA-mRNA interaction pairs may participate in floral transition. CONCLUSIONS: This study is the first to identify lncRNAs and their potential functions in floral transition, providing a starting point for detailed determination of the functions of lncRNAs in C. bungei.

Water, starch, and nuclear behavior in ray parenchyma during heartwood formation of Catalpa bungei 'Jinsi'.

Catalpa bungei 'Jinsi', a cultivar of C. bungei C. A. Mey., is valued for its heartwood with good overall mechanical properties, naturally durable and golden-yellow color. Little is known about heartwood formation in C. bungei 'Jinsi' trees. The behavior of starch, water, and nuclei was studied in the xylem tissue of C. bungei 'Jinsi' concerning aging in ray parenchyma cells. Blocks containing heartwood, golden zone, transition zone, and sapwood were collected from the stems of six C. bungei 'Jinsi' trees. The moisture content of the blocks was measured by oven drying. Changes in starch and nuclei in ray parenchyma were investigated in radial profiles from sapwood to heartwood blocks using microscopy and various staining techniques. The nuclear size and starch content gradually decreased to heartwood. While the horizontal distribution of moisture content of C. bungei 'Jinsi' was very varied, with the heartwood and golden zone being lower than sapwood but slightly higher than the transition zone. Starch grains were rare, but nuclei were still present in some ray parenchyma cells in the heartwood and golden zone. The nuclei showed irregular shape and elongation before disintegration. These results suggest that the most apparent change occurs in the transition zone, the critical location involved in forming C. bungei 'Jinsi' heartwood. Water and starch appear to be actively engaged in heartwood formation. The loss of function of ray parenchyma cells results from heartwood formation.

Genome-wide identification of DnaJ gene family in Catalpa bungei and functional analysis of CbuDnaJ49 in leaf color formation.

DnaJs are the common molecular chaperone proteins with strong structural and functional diversity. In recent years, only several DnaJ family members have been found to be able to regulate leaf color, and it remains to be explored whether there are other potential members that also regulate this character. Here, we identified 88 putative DnaJ proteins from Catalpa bungei, and classified them into four types according to their domain. Gene-structure analysis revealed that each member of CbuDnaJ family had same or similar exon-intron structure. Chromosome mapping and collinearity analysis showed that tandem and fragment duplication occurred in the process of evolution. Promoter analyses suggested that CbuDnaJs might be involved in a variety of biological processes. The expression levels of DnaJ family members in different color leaves of Maiyuanjinqiu were respectively extracted from the differential transcriptome. Among these, CbuDnaJ49 was the largest differentially expressed gene between the green and yellow sectors. Ectopic overexpression of CbuDnaJ49 in tobacco showed that the positive transgenic seedlings exhibited albino leaves, and the contents of chlorophyll and carotenoid were significantly reduced compared with those of wild type. The results suggested that CbuDnaJ49 played an important role in regulating leaf color. This study not only identified a novel gene of DnaJ family members regulating leaf color, but also provided new germplasm for landscaping.

Naphthoquinones from Catalpa bungei "Jinsi" as potent antiproliferation agents inducing DNA damage.

Structure-guided isolation of a CH2Cl2-soluble fraction of the heartwood of Catalpa bungei "Jinsi" provided two new naphthoquinones, 9-hydroxy-4-oxo-α-lapachone (1) and 6-hydroxy-4-oxo-α-lapachone (2), together with three undescribed ones (3-5) and six known ones (6-11). The structures were elucidated on the basis of spectroscopic methods including electronic circular dichroism calculation. The antiproliferative effects of these isolates were evaluated in human breast adenocarcinoma cells MCF7. (4R)-4,9-dihydroxy-α-lapachone (5) and (4S)-4,9-dihydroxy-α-lapachone (6) exhibited the significant activities with IC50 values of 2.19 and 2.41 µM, respectively. The structure-activity relationship of 1-11 in the antiproliferative assay was then discussed. The most potent 5 and 6 were found to induce cell arrest in G1 phage through DNA damage. The findings provided some valuable insights for the discovery and structural modification of α-lapachone as antiproliferative lead compounds against human breast adenocarcinoma cells.

Soil microbial communities response to different fertilization regimes in young Catalpa bungei plantation.

Fertilization is a fundamental aspect of global forest management that enhances forest productivity and drastically affects soil microbial communities. However, few studies have investigated the differences and similarities in the responses of below-ground microbial communities to different fertilization schemes. The effects of fertilization regimes on the composition and diversity of soil fungal and bacterial communities were investigated in a young Catalpa bungei plantation in Shandong Province, Eastern China. Soil microbial communities were assessed undergoing three types of fertilization: (i) no fertilization (CK), (ii) hole fertilization (HF), and (iii) the integration of water and fertilizer (WF). We further analyzed the effects of soil depth (i.e., 0-20 and 20-40 cm) on the structure of soil microbial communities. Our results indicated that the diversity of bacteria (e.g., Chao1 and Shannon indices) reduced undergoing fertilization, and WF had a higher negative impact on bacterial diversity than HF. A lower bacterial diversity was observed in the subsoil compared to the topsoil. In contrast to bacterial diversity, fungal diversity had a slightly increasing trend in the fertilized environments. The primary bacterial function was metabolism, which was independent of fertilization or soil depth. Among fungal functional guilds, symbiotic soil fungi decreased obviously in the fertilized stand, whereas saprotrophic fungi increased slowly. According to the structural equation models (SEM), the diversity and composition of bacterial and fungal communities were jointly regulated by soil nutrients (including N and P contents) directly affected by fertilization and soil layer. These findings could be used to develop management practices in temperate forests and help sustain soil microbial diversity to maintain long-term ecosystem function and services.

Transcriptomic, Proteomic, and Metabolic Profiles of Catalpa bungei Tension Wood Reveal New Insight Into Lignin Biosynthesis Involving Transcription Factor Regulation.

Lignin is a complex polymer in plant cell walls whose proportion is second only to that of cellulose and plays an important role in the mechanical properties of wood and stress resistance of plants. Here, we induced tension wood (TW) formation in Catalpa bungei by artificial bending and analyzed the lignin metabolism of the TW. LC-MS analysis showed that a significantly higher content of coniferyl aldehyde was observed in the TW cell wall than in the opposite wood (OW) and normal wood (NW) cell walls. TW had significantly lower contents of coniferyl alcohol than OW and NW. Raman spectroscopy results indicated that TW had lower total lignin than OW and NW. The transcription and translation levels of most of the differentially expressed genes (DEGs) involved in lignin monomer biosynthesis indicated upregulation in TW/OW and TW/NW. We found no significant difference in the transcription levels of three collision gases (CADs) between TW and OW or between NW, but their translation levels were significantly downregulated in TW, suggesting post-transcriptional control for CAD. We predicted and analyzed transcription factors that could target DEGs involved in lignin monomer biosynthesis in TW. Based on the analysis of the relationships of targeting and coexpression, we found that NAC (evm.model.group1.695) could potentially target 4CLs and CCoAOMT, that HD-Zip (evm.model.group7.1157) had potential targeting relationships with CCoAOMT, F5H, and CCR, and that their expression levels were significantly positive. It is speculated that the upregulation of NAC and HD-ZIP transcription factors activates the expression of downstream target genes, which leads to a significant increase in coniferyl aldehyde in TW. However, the decrease in total lignin in TW may be caused by the significant downregulation of CAD translation and the significant decrease in precursors (coniferyl alcohol). Whether the expression of CAD genes is regulated by post-transcriptional control and affects TW lignin metabolism needs further study.

A Bivariate Mapping Model Identifies Major Covariation QTLs for Biomass Allocation Between Leaf and Stem Growth of Catalpa bungei.

Biomass allocation plays a critical role in plant morphological formation and phenotypic plasticity, which greatly impact plant adaptability and competitiveness. While empirical studies on plant biomass allocation have focused on molecular biology and ecology approaches, detailed insight into the genetic basis of biomass allocation between leaf and stem growth is still lacking. Herein, we constructed a bivariate mapping model to identify covariation QTLs governing carbon (C) allocation between the leaves and stem as well as the covariation of traits within and between organs in a full-sib mapping population of C. bungei. A total of 123 covQTLs were detected for 23 trait pairs, including six leaf traits (leaf length, width, area, perimeter, length/width ratio and petiole length) and five stem traits (height, diameter at breast height, wood density, stemwood volume and stemwood biomass). The candidate genes were further identified in tissue-specific gene expression data, which provided insights into the genetic architecture underlying C allocation for traits or organs. The key QTLs related to growth and biomass allocation, which included UVH1, CLPT2, GAD/SPL, COG1 and MTERF4, were characterised and verified via gene function annotation and expression profiling. The integration of a bivariate Quantitative trait locus mapping model and gene expression profiling will enable the elucidation of genetic architecture underlying biomass allocation and covariation growth, in turn providing a theoretical basis for forest molecular marker-assisted breeding with specific C allocation strategies for adaptation to heterogeneous environments.

The complete chloroplast genome sequence of Catalpa bungei (Bignoniaceae): a high-quality timber species from China.

Catalpa bungei is an important resource of timber, belonging to the genus catalpa (Bignoniaceae). In this study, we sequenced complete chloroplast (cp) genome of C. bungei, using a NovaSeq 6000 sequencing platform. The genome of the C. bungei was 152,153 bp in length, including a large single-copy region (84,910 bp), a small single-copy region (12,664 bp), and two inverted repeats regions (30,285 bp). It encodes 126 genes, including 81 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Phylogenetic analyses were performed based on 15 cp genomes using the maximum likelihood (ML) method, supported that C. bungei was probably more closely related to C. speciosa. This study, the cp genome of C. bungei was assembled, which will provide more theoretical basis for determine the phylogenetic relationships of the Catalpa and related species.

Genome-wide analysis of the Catalpa bungei caffeic acid O-methyltransferase (COMT) gene family: identification and expression profiles in normal, tension, and opposite wood.

Caffeic acid O-methyltransferase (COMT) is an important protein that participates in lignin synthesis and is associated with the ratio of G-/S-type lignin in plants. COMTs are associated with the wood properties of forest trees; however, little known about the COMT family in Catalpa bungei, a valuable timber tree species in China . We performed a comprehensive analysis of COMT genes in the C. bungei genome by describing the gene structure and phylogenetic relationships of each family member using bioinformatics-based methods. A total of 23 putative COMT genes were identified using the conserved domain sequences and amino acid sequences of COMTs from Arabidopsis thaliana and Populus trichocarpa as probes. Phylogenetic analysis showed that 23 CbuCOMTs can be divided into three groups based on their structural characteristics; five conserved domains were found in the COMT family. Promoter analysis indicated that the CbuCOMT promoters included various cis-acting elements related to growth and development. Real-time quantitative polymerase chain reaction (PCR) analysis showed differential expression among CbuCOMTs. CbuCOMT2, 7, 8, 9, 10, 12, 13, 14, 21, and 23 were mainly expressed in xylem. Only CbuCOMT23 was significantly downregulated in tension wood and upregulated in opposite wood compared to normal wood. Our study provides new information about the CbuCOMT gene family and will facilitate functional characterisation in further research.

Comparative transcriptome analysis highlights the hormone effects on somatic embryogenesis in Catalpa bungei.

KEY MESSAGE: The major pathways and key events related to somatic embryo development in Catalpa bungei were illustrated by deep analysis of DEGs and quantification of hormone contents. Catalpa bungei C.A. Meyer is a valuable timber species, known as "The king of wood" in China. Due to the low propagation rate, somatic embryogenesis-based rapid propagation can regenerate a large number of new plants in a very short period of time and thus has great commercial value for this timber species. However, the mechanisms of somatic embryogenesis in C. bungei remain largely unclear so far. In our previous study, we established the vegetative propagation system in C. bungei using immature zygotic embryo as explants. Here, we further compared the transcriptional profiles and hormones contents between the embryogenic callus (EC) and non-embryogenic callus (NEC). RNA-seq analysis showed a total assembly of 73038 unigenes, and identified 12310 differentially expressed genes (DEGs) between EC and NEC. Also, six DEGs were chosen to verify the authenticity of the transcriptome sequencing results by qRT-PCR. Moreover, by using LC-MS approaches, we quantified various plant hormone contents and found that auxin and ABA were dramatically higher in EC than those in NEC. Accordingly, DEGs were enriched in plant hormone signaling pathways. Taken together, we highlight the hormone effects on somatic embryogenesis in a tree species, C. bungei. The use of certain genes as markers of embryogenesis induction in C. bungei regeneration process will provide new tools to pre-screen genotypes or tissue culture hormone combinations suitable for somatic embryo production. Our results provide theoretical references for the somatic embryogenesis mechanism and experimental bases for breeding and rapid propagation of C. bungei.

Physiological and transcriptional responses of Catalpa bungei to drought stress under sufficient- and deficient-nitrogen conditions.

Many semi-arid ecosystems are simultaneously limited by soil water and nitrogen (N). We conducted a greenhouse experiment to address how N availability impacts drought-resistant traits of Catalpa bungei C. A. Mey at the physiological and molecular level. A factorial design was used, consisting of sufficient-N and deficient-N combined with moderate drought and well-watered conditions. Seedling biomass and major root parameters were significantly suppressed by drought under the deficient-N condition, whereas N application mitigated the inhibiting effects of drought on root growth, particularly that of fine roots with a diameter <0.2 mm. Intrinsic water-use efficiency was promoted by N addition under both water conditions, whereas stable carbon isotope compositions (δ13C) was promoted by N addition only under the well-watered condition. Nitrogen application positively impacted drought adaptive responses including osmotic adjustment and homeostasis of reactive oxygen species, the content of free proline, soluble sugar and superoxide dismutase activity: all were increased upon drought under sufficient-N conditions but not under deficient-N conditions. The extent of abscisic acid (ABA) inducement upon drought was elevated by N application. Furthermore, an N-dependent crosstalk between ABA, jasmonic acid and indole acetic acid at the biosynthesis level contributed to better drought acclimation. Moreover, the transcriptional level of most genes responsible for the ABA signal transduction pathway, and genes encoding the antioxidant enzymes and plasma membrane intrinsic proteins, are elevated upon drought only under sufficient-N addition. These observations confirmed at the molecular level that major adaptive responses to drought are dependent on sufficient N nutrition. Although N uptake was decreased under drought, N-use efficiency and transcription of most genes encoding N metabolism enzymes were elevated, demonstrating that active N metabolism positively contributed drought resistance and growth of C. bungei under sufficient-N conditions.

Development and characterization of EST-SSR markers for Catalpa bungei (Bignoniaceae).

PREMISE OF THE STUDY: Catalpa bungei (Bignoniaceae) is a deciduous tree native to China. We developed microsatellite markers for C. bungei to investigate its population genetics. METHODS AND RESULTS: One hundred seventy-seven expressed sequence tag (EST)-simple sequence repeat (SSR) primer pairs were isolated and characterized using next-generation sequencing. Thirty of these primer pairs were polymorphic loci in 52 individuals of C. bungei. The number of alleles ranged from two to 18 with observed and expected heterozygosity values of 0.05-1.00 and 0.18-0.95, respectively. The fixation index ranged from -1.00 to 1.00 with an average of 0.32. No linkage disequilibrium was detected in any pair of loci. All markers showed good amplification results in four species (C. bungei, C. fargesii, C. duclouxii, and C. ovata) except three loci. CONCLUSIONS: These polymorphic markers are expected to be helpful in further studies on the systematics and phylogeography of C. bungei and related species.