BackgroundCatalpa 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.ResultsRestriction 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.ConclusionsThis 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.

15"Bairihua", a variety of the Catalpa bungei, has a large amount of flowers and a long flowering 16 period which make it an excellent material for flowering researches in trees. SPL is one of the hub 17 genes that regulate both flowering transition and development. Here, a SPL homologues CbuSPL9 18 was cloned using degenerate primers with RACE. Expression studies during flowering transition 19in Bairihua and ectopic expression in Arabidopsis showed that CbuSPL9 was functional similarly 20 with its Arabidopsis homologues. In the next step, we used Y2H to identify the proteins that could 21 interact with CbuSPL9. HMGA, an architectural transcriptional factor, was identified and cloned 22 for further research. BiFC and BLI showed that CbuSPL9 could form a heterodimer with 23CbuHMGA in the nucleus. The expression analysis showed that CbuHMGA had a similar 24 expression trend to that of CbuSPL9 during flowering in "Bairihua". Intriguingly, ectopic 25 expression of CbuHMGA in Arabidopsis would lead to aberrant flowers, but did not effect 26 flowering time. Taken together, our results implied a novel pathway that ChuSPL9 regulated 27 flowering development, but not flowering transition, with the participation of ChuHMGA. Further 28 investments need to be done to verify the details of this pathway. 29 Keywords: Catalpa bungei; Flowering; SPL; HMGA; Architectural transcriptional factor. 30 bungei is valuable as both a timber and an ornamental tree 1 . "Bairihua", which is a natural variety 37 of C. bungei, has been characterized for its especially short juvenile period, large number of 38 flowers and long flowering period. The flowering period of "Bairihua" is approximately 15 days, 39 and its accumulative flowering period reaches 100 days, which is very rare for woody plants 40(http://www.forestry.gov.cn/). "Bairihua" provides an excellent opportunity to evaluate the 41 flowering process of woody plants. 42Flowering is controlled by sophisticated regulatory networks 2-5 . Five major pathways are involved 43 in these processes, including the aging pathway 6 , gibberellin pathway 7-11 , photoperiod 44 pathway 12-16 , vernalization pathway [17][18][19] and autonomous pathway 20 . The SQUAMOSA 45 promoter-binding protein-LIKE (SPL) family of transcription factors (TFs) integrate multiple 46 pathways [21][22][23][24][25] . SPLs have been shown to regulate flowering time and flower organ development in 47 both herbs and woody plants, such as Gossypium hirsutum 26 , maize 27 , birch 28 , Prunus mume 29 , and 48Platanus acerifolia 30 . In the model plant Arabidopsis, AtSPLs have been shown to be a group of 49 dominant regulators of the flowering process 4,11,13,22,24,[31][32][33][34] . The overexpression of AtSPLs leads to 50 early flowering and abnormal inflorescence, and conversely, the inhibition of AtSPL expression 51 delays the occurrence of floral transition 21,[35][36][37] . As a group of TFs, SPLs regulate the expression 52 of other genes. Numerous downstream genes of SPLs have been identified; for example, AtSPL3 53 can...

In this study, the poplar doubled haploid (DH) plants were used as the experimental material to explore the huge phenotypic differences between homozygous DH plants and the paternal plants, and the molecular regulation mechanism of the differential phenotypes. In this experiment, through morphological and histological observation and statistics, we found that the double haploid plants had significantly reduced plant height and ground diameter, increased leaf aspect ratio, premature senescence phenotype of top bud, and significant changes in the shape and cell area of the shoot apical meristem. Significantly differentially expressed genes were obtained using RNA-seq transcriptome sequencing. They were subjected to GO enrichment and KEGG analysis. Transcription factors with key functions were screened out for qRT-PCR to verify gene expression changes to predict gene function. The results showed that after the IAA and ABA treatment, the expression levels of some hormone-responsive genes in wild type plants were significantly changed with different treatment time. In the dihaploid plants, the corresponding genes also changed to different degrees, which reflected the changes in the response of the dihaploid plants to hormones. Compared to in WT, the differential expressed genes in the double haploids were involved in multiple physiological process such as response to oxidative stress, response to salicylic acid, plant pathogen interaction, and plant hormone signal transduction. A TF–centered gene regulatory network for phytohormone synthesis and plant senescence was constructed with the expression patterns of differentially expressed transcription factors (TFs). This study increases researchers’ understanding of the regulation of poplar growth and development and provides new research ideas for the creation of new species of poplar.