A molecular assessment of the genetic model of spathe color inheritance in Anthurium andraeanum (Hort.)

A High-Resolution Linkage Map Construction and QTL Analysis for Morphological Traits in Anthurium (Anthurium andraeanum Linden)

Anthurium andraeanum Linden is a prominent ornamental plant belonging to the family Araceae and is cultivated worldwide. The morphology characteristics are crucial because they significantly impact ornamental values, commercial properties, and the efficiency of space utilization in production. However, only a few related investigations have been conducted in anthurium to date. In this study, an F1 genetic segregation population containing 160 progenies was generated through hybridization between potted and cut anthurium varieties. Fifteen morphological traits were assessed and revealed substantial levels of genetic variation and widespread positive correlation. Based on specific length amplified fragment (SLAF) sequencing technology, 8171 single nucleotide polymorphism (SNP) markers were developed, and the high-density linkage map of 2202.27 cM in length distributed on 15 linkage groups was constructed successfully, with an average distance of 0.30 cM. Using the inclusive composite interval mapping (ICIM) method, 59 QTLs related to 15 key morphological traits were successfully identified, which explained phenotypic variance (PVE) ranging from 6.21% to 17.74%. Thirty-three of those associated with 13 traits were designated as major QTLs with PVE > 10%. These findings offer valuable insights into the genetic basis of quantitative traits and are beneficial for molecular marker-assisted selection (MAS) in anthurium breeding.

Identification of key genes responsible for green and white colored spathes in Anthurium andraeanum (Hort.)

Modern anthuriums, Anthurium andraeanum (Hort.) are among the most popular flowering plants and widely used for interior decoration. Their popularity is largely attributed to the exotic spathes with different colors. Previous studies have reported color development in red spathe cultivars, but limited information is available on key genes regulating white and green colored spathes. This study analyzed anthocyanin, chlorophyll, and carotenoid contents as well as transcript differences in spathes of eight cultivars that differed in spathe colors ranging from red to white and green. Results showed that increased expression of a transcription factor AaMYB2 was associated with elevated levels of anthocyanin in spathes, but decreased expression of AaMYB2 and increased expression of AaLAR (leucoanthocyanidin reductase) and AaANR (anthocyanidin reductase) were accompanied with the accumulation of colorless proanthocyanidin, thus the white spathe. As to the green colored spathe, chlorophyll content in the green spathe cultivar was substantially higher than the other cultivars. Correspondingly, transcripts of chlorophyll biosynthesis-related genes AaHemB (porphobilinogen synthase) and AaPor (protochlorophyllide oxidoreductase) were highly upregulated but almost undetectable in white and red spathes. The increased expression of AaHemB and AaPor was correlated with the expression of transcription factor AaMYB124. Subsequently, qRT-PCR analysis confirmed their expression levels in nine additional cultivars with red, white, and green spathes. A working model for the formation of white and green spathes was proposed. White colored spathes are likely due to the decreased expression of AaMYB2 which results in increased expression of AaLAR and AaANR, and the green spathes are attributed to AaMYB124 enhanced expression of AaHemB and AaPor. Further research is warranted to test this working model.

Pantranscriptome combined with phenotypic quantification reveals germplasm kinship and regulation network of bract color variation in Bougainvillea

Bracts are the metamorphic non-flower organ in angiosperm plants. The variation of the color and shape of bracts was found to be neo-functionalized (i.e., similar to petals), garnering research interest as a pollinator attractor. Bougainvillea is known for its specialized, large, and colorful bracts, which contrast with its tiny colorless flowers. As a plant whose bracts vary greatly in terms of coloration, the molecular mechanisms for Bougainvillea bract coloration and polychroism are largely unknown. The lack of genomic information for Bougainvillea largely hinders studies into the evolution and genetic basis of bract color variation. In this study, a pan-transcriptome of bracts obtained from 18 Bougainvillea glabra accessions was employed to investigate the global population-level germplasm kinship and the gene regulation network for bract color variation. Our results showed that the bracts of B. glabra accessions have largely differentiated International Commission on Illumination (CIE) L-a-b values. Moreover, germplasm kinship detected using principal component analysis, phylogeny, and admixture analysis showed three optimal subgroups, two of them distinctly clustered, which were not directly correlated with bract color variation at the population level. Differentially expressed genes (DEGs) between accessions of high vs. low L-a-b values revealed several considerable upregulated genes related to bract color L-a-b variation. A weighted gene co-expression network was constructed, and eight co-expressed regulation modules were identified that were highly correlated with variation in bract CIE L-a-b color values. Several candidate DEGs and co-expressed hub genes (e.g., GERD, SGR, ABCA3, GST, CYP76AD1, CYP76C, and JAZ) that were tightly associated with bract color variation were eventually determined responsible for L-a-b colorations, which might be the core regulation factors contributing to the B. glabra bract color variation. This study provides valuable insights into the research on germplasm kinship, population-level pan-transcriptome expression profiles, and the molecular basis of color variation of key innovative bracts in horticultural Bougainvillea.

Integrated small RNA profiling and degradome analysis of Anthurium andraeanum cultivars with different-colored spathes

MicroRNAs (miRNAs) are known to play vital roles in coloration of leaves, flowers, and fruits in plants. However, their functions in spathe coloration are poorly known. Anthurium andraeanum is a popular ornamental plant with various spathe colors. In this study, small RNA and degradome libraries from three A. andraeanum cultivars with different-colored spathes were constructed and sequenced. Illumina sequencing resulted in 94 conserved miRNAs, and 34 novel miRNAs in total were then identified based on precursor sequences and hairpin structures. Differential expression analysis showed that 52, 51, and 49 miRNAs were differentially expressed in comparisons of orange- versus white-colored spathe, purple- versus white-colored spathe, and purple- versus orange-colored spathe, respectively. The expression patterns of miRNAs and their corresponding targets involved in spathe coloration were further analyzed, and displayed that miR156b and miR529 were highly abundant in the spathes with higher anthocyanin content. These two miRNAs co-targeted a gene encoding SPL17, which may function as a negative regulator in anthocyanin accumulation. In addition, miR408 was also abundantly expressed in purple- and orange-colored spathes, and its typical targets were also identified. This comprehensive integrated analysis provides insight into the miRNA-mediated genetic regulation in spathe coloration of A. andraeanum.

Comparative transcriptomic analysis reveals key components controlling spathe color in Anthurium andraeanum (Hort.)

Anthurium andraeanum (Hort.) is an important ornamental in the tropical cut-flower industry. However, there is currently insufficient information to establish a clear connection between the genetic model(s) proposed and the putative genes involved in the differentiation between colors. In this study, 18 cDNA libraries related to the spathe color and developmental stages of A. andraeanum were characterized by transcriptome sequencing (RNA-seq). For the de novo transcriptome, a total of 114,334,082 primary sequence reads were obtained from the Illumina sequencer and were assembled into 151,652 unigenes. Approximately 58,476 transcripts were generated and used for comparative transcriptome analysis between three cultivars that differ in spathe color (‘Sasha’ (white), ‘Honduras’ (red), and ‘Rapido’ (purple)). A large number of differentially expressed genes (8,324), potentially involved in multiple biological and metabolic pathways, were identified, including genes in the flavonoid and anthocyanin biosynthetic pathways. Our results showed that the chalcone isomerase (CHI) gene presented the strongest evidence for an association with differences in color and the highest correlation with other key genes (flavanone 3-hydroxylase (F3H), flavonoid 3’5’ hydroxylase (F3’5’H)/ flavonoid 3’-hydroxylase (F3’H), and leucoanthocyanidin dioxygenase (LDOX)) in the anthocyanin pathway. We also identified a differentially expressed cytochrome P450 gene in the late developmental stage of the purple spathe that appeared to determine the difference between the red- and purple-colored spathes. Furthermore, transcription factors related to putative MYB-domain protein that may control anthocyanin pathway were identified through a weighted gene co-expression network analysis (WGCNA). The results provided basic sequence information for future research on spathe color, which have important implications for this ornamental breeding strategies.

AaMYB3 interacts with AabHLH1 to regulate proanthocyanidin accumulation in Anthurium andraeanum (Hort.)-another strategy to modulate pigmentation

Proanthocyanidins (PAs), also known as "condensed tannins", are colorless metabolites produced through the flavonoid pathway that are involved in stress resistance in plants. Because PAs are involved in the anthocyanin biosynthetic pathway, they play a role in the modification of pigmentation conferred by anthocyanins in ornamental organs. In this study, we isolated the gene and functionally characterized an R2R3-MYB transcription factor (TF), AaMYB3, and a basic helix-loop-helix TF, AabHLH1, from Anthurium andraeanum (Hort.), a typical tropical flower. AaMYB3 is primarily expressed in the spathe and negatively correlates with anthocyanin accumulation. A complementation test in an Arabidopsis tt8 mutant showed that AabHLH1 successfully restores the PA-deficient seed coat phenotype. The ectopic overexpression of AaMYB3 alone or its coexpression with AabHLH1 in transgenic tobacco resulted in light pink or even pale-pink corolla limbs by reducing their anthocyanin levels and greatly enhancing their accumulation of PAs. This overexpression of the anthurium TF genes upregulated the late anthocyanin enzyme-encoding genes (NtDFR and NtANS) and the key PA genes (NtLAR and NtANR) in transgenic tobacco. The interaction between AaMYB3 and the AabHLH1 protein was confirmed using yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. In the developing red spathes of the cultivars "Vitara" and "Tropical", the expression of AaMYB3 was closely linked to PA accumulation, and AaMYB3 was coexpressed with AaCHS, AaF3H, AaDFR, AaANS, AaLAR, and AaANR. The expression pattern of AabHLH1 was similar to that of AaF3'H. Our results suggest that AaMYB3 and AabHLH1 are involved in the regulation of PA biosynthesis in anthurium and could potentially be used to metabolically engineer PA biosynthesis in plants.

Organ-specific transcriptome profiling of metabolic and pigment biosynthesis pathways in the floral ornamental progenitor species Anthurium amnicola Dressler

Anthurium amnicola Dressler possesses a number of desirable and novel ornamental traits such as a purple-colored upright spathe, profuse flowering, and floral scent, some of which have been introgressed into modern Anthurium cultivars. As a first step in identifying genes associated with these traits, the transcriptome from root, leaf, spathe, and spadix from an accession of A. amnicola was assembled, resulting in 28,019 putative transcripts representing 19,458 unigenes. Genes involved in pigmentation, including those for the metabolism of chlorophyll and the biosynthesis of carotenoids, phenylpropanoids, and flavonoids were identified. The expression levels of one MYB transcription factor was highly correlated with naringenin 3-dioxygenase (F3H) and dihydroflavonol-4-reductase (DFR) in leaves, whereas a bHLH transcription factor was highly correlated with flavonoid 3′-monooxygenase (F3′H) and a DFR in spathes, suggesting that these two transcription factors might regulate flavonoid and anthocyanin synthesis in A. amnicola. Gene sequence and expression data from four major organs of A. amnicola provide novel basal information for understanding the genetic bases of ornamental traits and the determinants and evolution of form and function in the Araceae.

Isolation and characterization of a R2R3-MYB transcription factor gene related to anthocyanin biosynthesis in the spathes of Anthurium andraeanum (Hort.)

KEY MESSAGE

A R2R3-MYB gene AaMYB2 was isolated from Anthurium andraeanum (Hort.) and was functionally characterized to be a positive transcriptional regulator for anthocyanin biosynthesis in the spathes and leaves. Spathe coloration is an important Anthurium andraeanum (Hort.) characteristic, which is mainly contributed by anthocyanins. R2R3-MYB transcription factors (TFs) are important regulators of anthocyanin biosynthesis in plants. Here we describe the identification and characterization of AaMYB2, a member in subgroup 6 of the R2R3-MYB TFs family, which correlated with anthocyanin biosynthesis in A. andraeanum. AaMYB2 was a nuclear-localization protein with positive transcriptional activity, and prominently expressed in the red spathes. Ectopic expression of AaMYB2 in tobacco led to anthocyanin accumulation and up-regulation of the early and late anthocyanin pathway genes, particularly NtDFR, NtANS, and NtUFGT, and the endogenous TF genes NtAn2 and NtAn1 in leaves. In the developing red spathes of 'Tropical' and 'Vitara', the expression of AaMYB2 was closely linked to anthocyanin accumulation, and co-expressed with AaCHS, AaF3H, and AaANS, the latter two of which were regarded as the potential targets of the R locus encoding a TF controlling spathe colors inheritance in anthurium. In addition, the transcription level of AaMYB2 in various cultivars with different color phenotypes showed that AaMYB2 was drastically expressed in the spathes from the red, pink, and purple cultivars, but hardly detected in the spathes from the white and green ones. Besides, AaMYB2 also showed higher expression in newly developmental leaves when anthocyanin was actively biosynthesized. Taken together, AaMYB2 positively related to anthocyanin biosynthesis in anthurium spathes and leaves, and appeared to regulate the expression of AaF3H, AaANS, and possibly AaCHS.

Chemotaxonomy of Hawaiian Anthurium cultivars based on multivariate analysis of phenolic metabolites

Thirty-six anthurium varieties, sampled from species and commercial cultivars, were extracted and profiled by liquid-chromatography-mass spectrometry (HPLC-MS). Three hundred fifteen compounds, including anthocyanins, flavonoid glycosides, and other phenolics, were detected from these extracts and used in chemotaxonomic analysis of the specimens. Hierarchical cluster analysis (HCA) revealed close chemical similarities between all the commercial standard cultivars, while tulip-shaped cultivars and species displayed much greater chemical variation. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) supported the results from HCA and were used to identify key metabolites characteristic of standard and tulip cultivars and to identify chemical markers indicative of a particular ancestry. Discriminating metabolites included embinin, 4, which was characteristic of standard-shaped spathes and indicated ancestry from Anthurium andraeanum, while isocytisoside 7-glucoside, 7, was found in the majority of tulip-shaped cultivars and suggested that Anthurium amnicola or Anthurium antioquiense had contributed to their pedigree.