Xin Zhao’s research while affiliated with China Agricultural University and other places

The gibberellins (GA) receptor GA INSENSITIVE DWARF1 (GID1) plays a central role in GA signal perception and transduction. The typical photoperiodic plant chrysanthemum (Chrysanthemum morifolium) only flowers when grown in short-day photoperiods. In addition, chrysanthemum flowering is also controlled by the aging pathway, but whether and how GAs participate in photoperiod- and age-dependent regulation of flowering remain unknown. Here, we demonstrate that photoperiod affects CmGID1B expression in response to GAs and developmental age. Moreover, we identified PHOTOLYASE/BLUE LIGHT RECEPTOR2 (PHR2), an atypical photocleavage synthase, as a CRYPTOCHROME-INTERACTING bHLH1 (CIB1) interactor with which it forms a complex in response to short days to activate CmGID1B transcription. Knocking down CmGID1B raised endogenous bioactive GA contents and GA signal perception, in turn modulating the expression of the aging-related genes MicroRNA156 (miR156) and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3 (SPL3). We propose that exposure to short days accelerates the juvenile-to-adult transition by increasing endogenous GA contents and response to GAs, leading to entry into floral transformation.

Chrysanthemum is one of the four major cut flowers in the world, with high ornamental and economic value. Fragrance is an important ornamental character of chrysanthemum flowers, especially those consumed as tea and other foods, and the flower fragrance is the major determinant of the commercial value of chrysanthemum cultivars. Currently, however, the research on chrysanthemum flower fragrance is mainly focused on the composition and content of fragrant compounds, and a clear classification of fragrance types is lacking. Here, we divided chrysanthemum fragrance into six categories based on sensory evaluation and determined the identity and content of fragrant compounds of chrysanthemum accessions representative of each fragrance type by GC-MS. In addition, we analyzed the conserved aromatic substances responsible for the fruity fragrance type chrysanthemum with multi-functional development potential, providing a theoretical basis for creating new chrysanthemum germplasm with specific fragrance types. The results of this study can accelerate the breeding process of chrysanthemum accessions with new fragrance types.

Chrysanthemum morifolium is one of the four major cut flowers in the world and has important ornamental and economic value. Flower fragrance is an important ornamental character of chrysanthemum, especially for tea and edible chrysanthemum, and the excellent fragrance determines its commercial value. At present, however, chrysanthemum is mostly chrysanthemum fragrance and medicinal fragrance, and the research on chrysanthemum flower fragrance mainly focuses on the composition and content of fragrancetic substances, and there is no clear classification of fragrance types. Here, we divided chrysanthemum fragrance into six categories by sensory evaluation, and detected the fragrance components and contents of every representative chrysanthemum with different fragrance types by GC-MS. In addition, we analyzed the genetic conservative substances of fruity fragrance chrysanthemum with multi-functional development potential, which provided a theoretical basis for creating new chrysanthemum germplasm with specific fragrance types, which was conducive to accelerating the biological breeding process of chrysanthemum with new fragrance types.

Strawflower (Helichrysum bracteatum) capitula have papery bracts and thus have the qualities of a naturally dried flower. The involucral bract cells have a secondary cell wall (SCW) of which a crucial component is lignin. Although the constituents of SCWs have been studied extensively in plants, little is known of the mechanism regulating SCW formation, especially lignin biosynthesis in the involucral bracts of strawflower. In this study, a homolog of NAC SECONDARY WALL THICKENING PROMOTING FACTOR 1, designated HbNST1, was identified as a positive regulator of lignin biosynthesis in strawflower. The transcript level of HbNST1 was the highest in the involucral bracts. Subcellular localization analysis indicated that HbNST1 was localized to the nucleus. Overexpression of HbNST1 in Chrysanthemum indicum promoted the expression of a gene related to lignin biosynthesis, a homolog of cinnamyl alcohol dehydrogenase, designated CiCAD, suggesting that HbNST1 was associated with the accumulation of lignin in the SCW of the involucral bracts. Taken together, the results suggested that HbNST1 positively regulated lignin accumulation in the involucral bracts and mediated the expression of lignin biosynthesis-related genes in strawflower.

Chrysanthemum (Chrysanthemum morifolium) is well known as a photoperiod-sensitive flowering plant. However, it has also evolved into a temperature-sensitive ecotype. Low temperature can promote the floral transition of the temperature-sensitive ecotype, but little is known about the underlying molecular mechanisms. Here, we identified CmMAF2 (MADS AFFECTING FLOWERING 2), a putative MADS-box gene, which induces floral transition in response to low temperatures independent of day length conditions in this ecotype. CmMAF2 was shown to bind to the promoter of the GA biosynthesis gene, CmGA20ox1, and to directly regulate the biosynthesis of bioactive GA1 and GA4 . The elevated bioactive GAs activated CmLFY (LEAFY) expression, ultimately initiating floral transition. In addition, CmMAF2 expression in response to low temperatures was directly activated by CmC3H1, a CCCH-type zinc-finger protein upstream. In summary, our results reveal that the CmC3H1-CmMAF2 module regulates the flowering time in response to low temperatures by regulating GA biosynthesis in the temperature-sensitive chrysanthemum ecotype.

The carotenoids biosynthesis pathway in plants has been studied extensively, yet little is known about the regulatory mechanisms underlying this process, especially for ornamental horticulture plants. In this study, a natural variation of chrysanthemum with orange coloration was identified and compared with the wild type with pink coloration; the content and component of carotenoids were largely enriched in the mutant with orange coloration. CmCCD4a-5, the DNA sequence in both ‘Pink yan’ and the mutant, was identified and shown to function as a carotenoid degradation enzyme. Compared with ‘Pink yan’, the mutant shows lower expression level of CmCCD4a-5. Furthermore, CmGATA4 was found to have an opposite expression trend to CmCCD4a-5, and it could directly bind with the CmCCD4a-5 promoter. Taken together, this study demonstrates that CmGATA4 acts as a negative regulator of CmCCD4a-5 and, furthermore, low expression of CmCCD4a-5 resulted in carotenoid accumulation in the mutant.

Drought is a major abiotic stress that limits plant growth and development. Adaptive mechanisms have evolved to mitigate drought stress, including the capacity to adjust water loss rate and to modify the morphology and structure of the epidermis. Here, we show that the expression of CmNF‐YB8, encoding a nuclear factor Y (NF‐Y) B‐type subunit, is lower under drought conditions in chrysanthemum (Chrysanthemum morifolium). Transgenic chrysanthemum lines in which transcript levels of CmNF‐YB8 were reduced by RNA interference (CmNF‐YB8‐RNAi) exhibited enhanced drought resistance relative to control lines, whereas lines overexpressing CmNF‐YB8 (CmNF‐YB8‐OX) were less tolerant to drought. Compared to wild type (WT), CmNF‐YB8‐RNAi plants showed reduced stomatal opening and a thicker epidermal cuticle that correlated with their water loss rate. We also identified genes involved in stomatal adjustment (CBL‐interacting protein kinase 6, CmCIPK6) and cuticle biosynthesis (CmSHN3) that are more highly expressed in CmNF‐YB8‐RNAi lines than in WT, CmCIPK6 being a direct downstream target of CmNF‐YB8. Virus‐induced gene silencing of CmCIPK6 or CmSHN3 in the CmNF‐YB8‐RNAi background abolished the effects of CmNF‐YB8‐RNAi on stomatal closure and cuticle deposition, respectively. CmNF‐YB8 thus regulates CmCIPK6 and CmSHN3 expression to alter stomatal movement and cuticle thickness in the leaf epidermis, thereby affecting drought resistance.

Volatile composition is an important feature that determines flavor, which actively affects the overall evaluation of chrysanthemum tea. In this study, HS-GC-IMS (headspace-gas chromatography-ion mobility spectrometry) was performed to characterize the volatile profiles of different chrysanthemum tea subtypes. Forty-seven volatiles of diverse chemical nature were identified and quantified. Partial least squares discriminant analysis (PLS-DA) revealed that four chrysanthemum teas were distinct from each other based on their volatile compounds. Furthermore, this work provides reference methods for detecting novel volatile organic compounds in chrysanthemum tea plants and products.

Drought is an environmental factor that can severely influence plant development and distribution, and greatly affect the yield and economic value of crops. We characterized CmBBX19 , a BBX family subgroup IV member gene, from the transcriptome database of Chrysanthemum morifolium in response to drought stress. Drought stress and ABA treatments downregulated the expression of CmBBX19 . We generated CmBBX19 ‐overexpressing (CmBBX19 ‐OX) lines and CmBBX19 ‐suppressing lines (CmBBX19 ‐RNAi), and found that suppressed expression of CmBBX19 led to enhanced drought tolerance compared with the wild‐type (WT) controls, while CmBBX19 ‐OX lines exhibited reduced drought tolerance. Downstream gene analysis showed that CmBBX19 modulates drought tolerance mainly through inducing changes in the expression of ABA‐dependent pathway genes, including protective protein, redox balance, and cell wall biogenesis genes, such as responsive to ABA 18 (RAB18 ), peroxidase 12 (PRX12 ), and cellulose synthase‐like protein G2 (CSLG2 ). Moreover, CmBBX19 was shown to interact with CmABF3, a master ABA signaling component, to suppress expression of these downstream genes. We conclude that BBX19‐ABF3 module functions in the regulation of drought tolerance of chrysanthemum through ABA dependent pathway.