Functional Analysis of a Cotton TPX2-like Gene, GbTPX2-35, in Regulating Fiber Cell Development and Strength in Gossypium barbadense

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.