Genome-Wide Analysis of MADS-Box Gene Family Reveals CjSTK as a Key Regulator of Seed Abortion in Camellia japonica.

The plant MADS-box transcription factor family is a major regulator of plant flower development and reproduction, and the AGAMOUS-LIKE11/SEEDSTICK (AGL11/STK) subfamily plays conserved functions in the seed development of flowering plants. Camellia japonica is a world-famous ornamental flower, and its seed kernels are rich in highly valuable fatty acids. Seed abortion has been found to be common in C. japonica, but little is known about how it is regulated during seed development. In this study, we performed a genome-wide analysis of the MADS-box gene the in C. japonica genome and identified 126 MADS-box genes. Through gene expression profiling in various tissue types, we revealed the C/D-class MADS-box genes were preferentially expressed in seed-related tissues. We identified the AGL11/STK-like gene, CjSTK, and showed that it contained a typical STK motif and exclusively expressed during seed development. We found a significant increase in the CjSTK expression level in aborted seeds compared with normally developing seeds. Furthermore, overexpression of CjSTK in Arabidopsis thaliana caused shorter pods and smaller seeds. Taken together, we concluded that the fine regulation of the CjSTK expression at different stages of seed development is critical for ovule formation and seed abortion in C. japonica. The present study provides evidence revealing the regulation of seed development in Camellia.

Photocatalytic Reduction of Perrhenate and Pertechnetate in a Strongly Acidic Aqueous Solution.

Pertechnetate (99TcO4-), a physiologically toxic radioactive anion, is of great concern due to its high mobility in environmental contamination remediation. Although the soluble oxyanion can be photoreduced to sparingly soluble TcO2·nH2O, its effective removal from a strongly acidic aqueous solution remains a challenge. Here, we found that low-crystalline nitrogen-doped titanium oxide (N-TiO2, 0.6 g L-1) could effectively uptake perrhenate (ReO4-, 10 mg L-1, a nonradioactive surrogate for TcO4-) with 50.8% during 360 min under simulated sunlight irradiation at pH 1.0, but P25 and anatase could not. The nitrogen active center formed by trace nitrogen doping in N-TiO2 can promote the separation and transfer of photogenerated carriers. The positive valence band value of N-TiO2 is slightly higher than those of P25 and anatase, which means that the photogenerated holes have a stronger oxidizability. These holes are involved in the formation of strong reducing •CO2- radicals from formic acid oxidation. The active radicals convert ReO4- to Re(VI), which is subsequently disproportionated to Re(IV) and Re(VII). Effective photocatalytic reduction/removal of Re(VII)/Tc(VII) is performed on the material, which may be considered a potential and convenient strategy for technetium decontamination and extraction in a strongly acidic aqueous solution.

Genomics insights into flowering and floral pattern formation: regional duplication and seasonal pattern of gene expression in Camellia.

BACKGROUND: The formation and domestication of ornamental traits are influenced by various aspects, such as the recognition of esthetic values and cultural traditions. Camellia japonica is widely appreciated and domesticated around the world mainly due to its rich variations in ornamental traits. Ornamental camellias have a diverse range of resources, including different bud variations from Camellia spp. as well as inter- and intra- specific hybridization. Despite research on the formation of ornamental traits, a basic understanding of their genetics and genomics is still lacking. RESULTS: Here, we report the chromosomal-level reference genome of C. japonica through combining multiple DNA-sequencing technologies and obtain a high-density genetic linkage map of 4255 markers by sequencing 98 interspecific F1 hybrids between C. japonica and C. chekiangoleosa. We identify two whole-genome duplication events in C. japonica: one is a shared ancient γ event, and the other is revealed to be specific to genus Camellia. Based on the micro-collinearity analysis, we find large-scale segmental duplication of chromosome 8, resulting to two copies of the AGAMOUS loci, which may play a key role in the domestication of floral shapes. To explore the regulatory mechanisms of seasonal flowering, we have analyzed year-round gene expression patterns of C. japonica and C. azalea-a sister plant of continuous flowering that has been widely used for cross breeding. Through comparative analyses of gene co-expression networks and annual gene expression patterns, we show that annual expression rhythms of some important regulators of seasonal growth and development, including GIGANTEA and CONSTANS of the photoperiod pathway, have been disrupted in C. azalea. Furthermore, we reveal that the distinctive expression patterns of FLOWERING LOCUS T can be correlated with the seasonal activities of flowering and flushing. We demonstrate that the regulatory module involved in GIGANTEA, CONSTANS, and FLOWERING LOCUS T is central to achieve seasonality. CONCLUSIONS: Through the genomic and comparative genomics characterizations of ornamental Camellia spp., we propose that duplication of chromosomal segments as well as the establishment of gene expression patterns has played a key role in the formation of ornamental traits (e.g., flower shape, flowering time). This work provides a valuable genomic platform for understanding the molecular basis of ornamental traits.

Small RNA profiling reveals that an ovule-specific microRNA, cja-miR5179, targets a B-class MADS-box gene in Camellia japonica.

BACKGROUND AND AIMS: The functional specialization of microRNA and its target genes is often an important factor in the establishment of spatiotemporal patterns of gene expression that are essential to plant development and growth. In different plant lineages, understanding the functional conservation and divergence of microRNAs remains to be explored. METHODS: To identify small regulatory RNAs underlying floral patterning, we performed a tissue-specific profiling of small RNAs in various floral organs from single and double flower varieties (flowers characterized by multiple layers of petals) in Camellia japonica. We identified cja-miR5179, which belongs to a deeply conserved microRNA family that is conserved between angiosperms and basal plants but frequently lost in eudicots. We characterized the molecular function of cja-miR5179 and its target - a B-function MADS-box gene - through gene expression analysis and transient expression assays. KEY RESULTS: We showed that cja-miR5179 is exclusively expressed in ovule tissues at the early stage of floral development. We found that cja-miR5179 targets the coding sequences of a DEFICIENS-like B-class gene (CjDEF) mRNA, which is located in the K motif of the MADS-box domain; and the target sites of miR5179/MADS-box were consistent in Camellia and orchids. Furthermore, through a petal transient-expression assay, we showed that the BASIC PENTACYSTEINE proteins bind to the GA-rich motifs in the cja-miR5179 promoter region and suppresses its expression. CONCLUSIONS: We propose that the regulation between miR5179 and a B-class MADS-box gene in C. japonica has a deep evolutionary origin before the separation of monocots and dicots. During floral development of C. japonica, cja-miR5179 is specifically expressed in the ovule, which may be required for the inhibition of CjDEF function. This work highlights the evolutionary conservation as well as functional divergence of small RNAs in floral development.

Characterizations of a Class-I BASIC PENTACYSTEINE Gene Reveal Conserved Roles in the Transcriptional Repression of Genes Involved in Seed Development.

The developmental regulation of flower organs involves the spatio-temporal regulation of floral homeotic genes. BASIC PENTACYSTEINE genes are plant-specific transcription factors that is involved in many aspects of plant development through gene transcriptional regulation. Although studies have shown that the BPC genes are involved in the developmental regulation of flower organs, little is known about their role in the formation of double-flower due. Here we characterized a Class I BPC gene (CjBPC1) from an ornamental flower-Camellia japonica. We showed that CjBPC1 is highly expressed in the central whorls of flowers in both single and doubled varieties. Overexpression of CjBPC1 in Arabidopsis thaliana caused severe defects in siliques and seeds. We found that genes involved in ovule and seed development, including SEEDSTICK, LEAFY COTYLEDON2, ABSCISIC ACID INSENSITIVE 3 and FUSCA3, were significantly down-regulated in transgenic lines. We showed that the histone 3 lysine 27 methylation levels of these downstream genes were enhanced in the transgenic plants, indicating conserved roles of CjBPC1 in recruiting the Polycomb Repression Complex for gene suppression.

The genome of oil-Camellia and population genomics analysis provide insights into seed oil domestication.

BACKGROUND: As a perennial crop, oil-Camellia possesses a long domestication history and produces high-quality seed oil that is beneficial to human health. Camellia oleifera Abel. is a sister species to the tea plant, which is extensively cultivated for edible oil production. However, the molecular mechanism of the domestication of oil-Camellia is still limited due to the lack of sufficient genomic information. RESULTS: To elucidate the genetic and genomic basis of evolution and domestication, here we report a chromosome-scale reference genome of wild oil-Camellia (2.95 Gb), together with transcriptome sequencing data of 221 cultivars. The oil-Camellia genome, assembled by an integrative approach of multiple sequencing technologies, consists of a large proportion of repetitive elements (76.1%) and high heterozygosity (2.52%). We construct a genetic map of high-density corrected markers by sequencing the controlled-pollination hybrids. Genome-wide association studies reveal a subset of artificially selected genes that are involved in the oil biosynthesis and phytohormone pathways. Particularly, we identify the elite alleles of genes encoding sugar-dependent triacylglycerol lipase 1, ß-ketoacyl-acyl carrier protein synthase III, and stearoyl-acyl carrier protein desaturases; these alleles play important roles in enhancing the yield and quality of seed oil during oil-Camellia domestication. CONCLUSIONS: We generate a chromosome-scale reference genome for oil-Camellia plants and demonstrate that the artificial selection of elite alleles of genes involved in oil biosynthesis contributes to oil-Camellia domestication.

Transcriptome and Degradome Profiling Reveals a Role of miR530 in the Circadian Regulation of Gene Expression in Kalanchoë marnieriana.

Crassulacean acid metabolism (CAM) is an important photosynthetic pathway for plant adaptation to dry environments. CAM plants feature a coordinated interaction between mesophyll and epidermis functions that involves refined regulations of gene expression. Plant microRNAs (miRNAs) are crucial post-transcription regulators of gene expression, however, their roles underlying the CAM pathway remain poorly investigated. Here, we present a study characterizing the expression of miRNAs in an obligate CAM species Kalanchoë marnieriana. Through sequencing of transcriptome and degradome in mesophyll and epidermal tissues under the drought treatments, we identified differentially expressed miRNAs that were potentially involved in the regulation of CAM. In total, we obtained 84 miRNA genes, and eight of them were determined to be Kalanchoë-specific miRNAs. It is widely accepted that CAM pathway is regulated by circadian clock. We showed that miR530 was substantially downregulated in epidermal peels under drought conditions; miR530 targeted two tandem zinc knuckle/PLU3 domain encoding genes (TZPs) that were potentially involved in light signaling and circadian clock pathways. Our work suggests that the miR530-TZPs module might play a role of regulating CAM-related gene expression in Kalanchoë.