Ruihong Zeng

Chrysanthemum morifolium is an important ornamental crop whose flowering is strictly regulated by photoperiod. However, the molecular mechanisms linking photoperiod signals to floral meristem identity and organ development in Asteraceae remain unclear. In this study, we identified and characterized CmAFL1, a FUL-like MADS-box gene specific to the Asteraceae family, in the short-day cultivar ‘Jinba’. CmAFL1 expression is upregulated under short-day conditions, primarily expressed in the shoot apical meristem during flower bud differentiation and predominantly in the receptacle during organ development. RNA interference-mediated silencing of CmAFL1 resulted in delayed flowering, arrested inflorescence development, malformed tubular florets, plant dwarfism, and excessive lateral branching, indicating its pleiotropic roles in flowering time, plant architecture, and floral organ patterning. At the molecular level, yeast one-hybrid assays revealed that the photoperiod pathway transcription factor CmCOL4 directly binds to the promoter region of CmAFL1. Furthermore, yeast one-hybrid and dual-luciferase assays confirmed that CmAFL1 directly interacts with and activates the promoter of the E-class floral organ identity gene CmSEP3. Together, our findings identify a novel transcriptional regulatory module CmCOL4-CmAFL1-CmSEP3 that potentially links photoperiod signaling to floral meristem identity and organ specification in Chrysanthemums. While further in planta validation is warranted, these findings provide novel insights into photoperiodic flowering regulation in Asteraceae and may serve as a theoretical foundation for molecular breeding strategies targeting flowering time manipulation in ornamental Chrysanthemums.

Background/Objectives: Tubulins (Tub) are central components of microtubules, but intraspecific variation and developmental expression of the Tub family in Gossypium barbadense remain poorly characterized. This study aimed to characterize the GbTub family using a pan-genome framework and identify candidates associated with fiber development and strength. Methods: A total of 50 GbTub genes were identified in the G. barbadense 3-79 reference genome, and their orthologous presence–absence patterns were subsequently assessed across 12 additional G. barbadense accessions. Phylogenetic, presence–absence variation (PAV), Ka/Ks, structural variation (SV), RNA-seq, RT-qPCR, co-expression, and GO enrichment analyses were integrated. Results: Among the 50 reference-defined GbTub genes, 43 were classified as core genes, 6 as near-core genes, and 1 as an accessory gene, and the encoded proteins were classified into α-, β-, and γ-tubulin clades. All genes showed Ka/Ks < 1. Twenty-three GbTub genes differed between the fiber-strength-contrasting accessions 5917 and PimaS-7, and representative expression trends were supported by RT-qPCR. Network analysis prioritized 10 GbTub candidates based on degree centrality. GbTub21 was the sole SV-associated GbTub gene displaying significant differential expression between accessions harboring versus lacking the corresponding SV. Non-Tub neighbors of the candidate hub genes were enriched for cytoskeletal, intracellular-transport, and plasma-membrane functions. Conclusions: The pan-genome analysis reveals strong conservation with limited intraspecific variation in the GbTub family. Co-expression profiles nominate candidates associated with fiber secondary-wall development, and their causal contribution to fiber strength awaits functional dissection.

Background/Objectives: Among cotton species, Gossypium barbadense produces the strongest fibers. Examining cytoskeletal dynamics in single epidermal cells of G. barbadense ovules offers a direct approach to investigating fiber quality. Microtubules are major cytoskeletal components whose organization and dynamics are precisely regulated by microtubule-associated proteins (MAPs). However, information on the TPX2 family remains limited, and characterizing its features in G. barbadense is critical to clarifying the role of TPX2 family members in fiber strength formation. Methods: Using the Arabidopsis thaliana TPX2 sequence as a reference, 40, 49, 26, and 26 TPX2 family members were identified in the genomes of G. barbadense, Gossypium hirsutum, Gossypium arboreum, and Gossypium raimondii, respectively. We further analyzed the expression pattern of GbTPX2-35 and validated its function via virus-induced gene silencing (VIGS). Results: In G. barbadense, GbTPX2-35 (Gbar_D11G59825.1) was significantly upregulated in fiber samples of the parental lines at 25 days post-anthesis, and this expression pattern was further validated in G. barbadense lines with extreme fiber strength phenotypes. Next, VIGS-mediated silencing of GbTPX2-35 downregulated the transcript levels of cellulose synthase and microtubule-related protein genes, a finding further validated by mature fiber strength phenotypic data. Conclusions: This study preliminarily validated a pathway in which GbTPX2-35 regulates fiber strength by coordinating cellulose biosynthesis with microtubule cytoskeleton dynamics, providing valuable candidate genes and theoretical support for molecular breeding of high-strength cotton fibers.