The nectar spur is an important feature of pollination and ecological adaptation in flowering plants, and it is a key innovation to promote species diversity in certain plant lineages. The development mechanism of spurs varies among different plant taxa. As one of the largest angiosperm genera, we have little understanding of the mechanism of spur development in Impatiens. Here, we investigated the initiation and growth process of spurs of Impatiens uliginosa based on histology and hormone levels, and the roles of AUXIN BINDING PROTEIN (ABP) and extensin (EXT) in spur development were explored. Our results indicate that the spur development of I. uliginosa is composed of cell division and anisotropic cell elongation. Imbalances in spur proximal-distal cell division lead to the formation of curved structures. Endogenous hormones, such as auxin and cytokinins, were enriched at different developmental stages of spurs. IuABP knockdown led to an increase in spur curves and distortion of morphology. IuEXT knockdown resulted in reduced spur length and loss of curve and inner epidermal papillae structures. This study provides new insights into the mechanism of spur development in core eudicots.

One of the most important characteristics of ornamental plants is leaf color, which enhances the color of plant landscapes and attracts pollinators for reproduction. The leaves of Impatiens hawkeri ‘Sakimp005’ are initially green, then the middle part appears yellow, then gradually become white, while the edge remains green. In the study, leaves of I. hawkeri ‘Sakimp005’, in four developmental stages (S1-G, S2-C, S3-C, and S4-C), were selected for the determination of pigment content, chromaticity values, integrative metabolomics, and transcriptomics analyses. The carotenoid content of leaves varied significantly and regularly at four stages, and the colorimetric values corroborated the phenotypic observations. The results of integrative metabolomics and transcriptomics analysis show that the accumulation of two carotenoids (lutein and zeaxanthin), to different degrees in the leaves of I. hawkeri ‘Sakimp005’ at four stages, led to the vary yellowing phenomenon. We speculated that the carotenoid biosynthesis (containing two branches: α-branch and β-branch) in leaves by IhLUT1 and IhLUT5 in the α-branch and IhBCH2 genes in the β-branch differed. These findings provide a molecular basis for Impatiens plants’ leaf color breeding and improve the knowledge of the leaf color mechanism.

Impatiens uliginosa is a plant of the Impatiens, with peculiar flowers. In this study, we combined morphogenesis and molecular biology to explore its development of flowers. An analysis of basic observational data and paraffin sectioning showed that it took approximately 13 d for the floral organs to differentiate. An analysis of the development of inflorescences and floral organs by scanning electron microscopy showed that the inflorescence of I. uliginosa is a spiral raceme. The floral organs differentiated in the following order: lateral sepals (Ls), posterior sepal (Ps), anterior sepals (As), anterior petal (Ap), lateral petals (Lp), stamens (St) and gynoecium (Gy). I. uliginosa was found to have four sepals, and the connate stamens are caused by the fusion and growth of filament appendages. The results of fluorescence quantification and virus-induced gene silencing showed that I. uliginosa had its own unique model for flower development, and there was functional diversity of IuAP1 and IuDEF. Among them, IuAP1 controls the formation of bract s (Br), regulates the morphogenesis of posterior sepal, controls the anthocyanin precipitation of the anterior petals and the formation of lateral petals. IuDEF regulates the morphogenesis of lateral sepals, the length of development of the spur, and controls the size of yellow flower color plaques of the lateral petals. In this study, the process of flower development and the function of flower development genes of I. uliginosa were preliminarily verified. This study provides basic guidance and new concepts that can be used to study the development of Impatiens flowers.

Flower color is a major feature of ornamental plants, and the rich flower color of plants is an important factor in determining their ornamental and economic values, so flower color is an important research target for gardening and horticulture breeders at home and abroad. Our research group collected four colors of Impatiens uliginosa (white, pink, red, and deep red) during the collection of germplasm resources in the field. In this study, we analyzed the transcriptomes of the four flower colors of I. uliginosa by using RNA-Seq technology. The transcriptomes were screened to identify candidate genes related to flower color, and the coloring mechanisms of four flower colors were revealed at the molecular level. The main findings were as follows: (1) The number of the four different transcripts ranged from 64,723 to 93,522 and contained a total of 100,705 unigenes. (2) The analysis of differentially expressed genes revealed structural genes including C4H, FLS, PAL, and ANS and transcription factors including MYB, MYB-related, AP2-EREBP, and bHLH. (3) Among the four flower colors of I. uliginosa, the C4H1 gene had the highest expression in pink flowers, and the C4H2 gene had the highest expression in red flowers. This indicated that C4H genes positively regulated the red flower color of I. uliginosa. However, FLS expression was the highest in white flowers, and with deepening flower color, FLS gene expression gradually weakened, acting as a negative regulator. The results of this study could lay the theoretical foundation for investigating the mechanism of coloration and flower color variation in I. uliginosa.

Impatiens is a genus of functional herbaceous plants in the Balsaminaceae, which are not only of great ornamental value and one of the world’s top three flower bedding plants but also have a wide range of medicinal and edible uses. Currently, the taxonomy and phylogenetic relationships of Impatiens species are still controversial. In order to better understand their chloroplast properties and phylogenetic evolution, nine Impatiens plants (Impatiens repens, Impatiens rectirostrata, Impatiens baishaensis, Impatiens rostellata, Impatiens faberi, Impatiens oxyanthera, Impatiens tienchuanensis, Impatiens blepharosepala, Impatiens distracta) were sequenced, and their complete chloroplast genomes were analysed. Nine species of Impatiens chloroplast genomes ranged in length from 150,810 bp (I. rectirostrata) to 152,345 bp (I. blepharosepala). The chloroplast genomes were all typical circular DNA molecules, and the GC content in each region was consistent with the published chloroplast genomes of Impatiens plants. The results showed that the seven mutational hotspots (trnL-UAG, ndhG, ycf1, ccsA, rrn23, trnA-UGC, and ycf2) could be used as supporting data for further analyses of the phylogenetic tree and species identification. In addition, the results of the phylogenetic tree support that Balsaminaceae is a monophyletic taxon, and that Hydrocera triflora is at the base of the branch, is the original species of Balsaminaceae, and is in a sister group relationship with Impatiens species. The results of this paper enrich the data of Impatiens chloroplast genomes, and the availability of these chloroplast genomes will provide rich genetic information for species identification, thus enhancing the taxonomic accuracy and phylogenetic resolution of Impatiens, and further promoting the investigation and rational use of Impatiens plant resources.

The complete chloroplast genome sequence of Impatiens hawker, a widely cultivated horticultural species in the world is 151,692 bp, with a typical quadripartite structure including a pair of inverted repeat (IRs, 25,584 bp) regions separated by a small single copy (SSC, 17,494 bp) region and a large single copy (LSC, 83,029 bp) region. The overall GC content of I. hawker plastid genome was 36.8%. The whole chloroplast genome contains 135 genes, including 89 protein-coding genes (PCGs), 38 transfer RNA genes(tRNAs), and 8 ribosomal RNA genes (rRNAs). Among these genes, 15 genes have one intron and 2 genes contain two introns. To investigate its evolution status, the phylogenetic tree based on APGIII reveal that there are close relationships to the same genus species I. uliginosa and I. piufanensis.