Abstract :
[en] Cotton is the most important natural fiber crop and serves as an ideal model system
for studying plant epidermal cell differentiation and single-cell polar elongation.
Because cotton fibers and trichomes on vegetative organs share a common epidermal
origin, combined investigations into their genetic basis and molecular mechanisms
can deepen our understanding of the formation of important agronomic traits in cotton. This dissertation focuses on the genetic dissection of cotton fiber quality- and yield related traits, as well as the molecular regulatory mechanisms underlying long
trichome formation and elongation. A combination of high-density genetic map
construction, QTL mapping, comparative genomics, transcriptome analysis, DAP-seq,
yeast one/two-hybrid assays, EMSA, dual-luciferase assays, VIGS, and genetic
transformation was used in this study. First, a recombinant inbred line (RIL) population derived from a cross between the upland cotton variety SIMIAN-3 and the upland cotton material Y1 (which contains introgression fragments from Gossypium barbadense) was constructed. Using GBS-SNP markers, a high-density genetic map containing 7,730 markers with a total genetic distance of 2,784.2 cM was developed. Plant architecture, fiber yield, and fiber quality-related traits were evaluated under multiple environmental conditions. A total of 58 QTLs were identified, among which 47 were stable QTLs, mainly distributed on chromosomes chr-A07, chr-D06, and chr-D07.
Furthermore, BZIP043 and SEP2 were screened as candidate genes associated with
seed index, providing a genetic basis for the coordinated improvement of cotton fiber
quality and yield. Second, the CPR5 gene family was systematically characterized across different genome backgrounds in the Gossypium genus, revealing that this family is highly conserved during cotton evolution. Combined with phylogenetic analysis, gene structure, cis-element prediction, co-expression networks, and expression profiling, GheCPR5.1 was identified as a key candidate gene closely related to trichome development. VIGS results further demonstrated that silencing GheCPR5.1 significantly reduced the number of long trichomes, indicating a positive role for CPR5 in cotton trichome elongation. Furthermore, a comparative survey of trichome phenotypes across 37 Gossypium species revealed that long trichomes (>1000 μm) are rare, occurring only in a few species, and are predominantly associated with low-latitude habitats characterized by high temperature, high radiation, and relatively dry summers. Using an F₂:₄ population derived from the long-trichome accession Dianya-10 and the short trichome accession A1a-lz, two major QTLs related to long trichomes were mapped. Combined with stage-specific transcriptome analysis, GaHDG11 and GaCPR5 were prioritized as important candidate regulators. Molecular interaction and functional analyses showed that GaHD1 and GaHDG11 form an upstream regulatory module; GaHDG11 directly binds to and activates both upstream and downstream cis-elements of GaZHD2; and GaZHD2 further binds to a 126-bp InDel region within the GaCPR5 promoter to activate its expression, with the PB motif serving as the 5 Genetic and molecular regulation of cotton epidermal cell specialization major responsive element. Notably, this 126-bp insertion allele was significantly enriched in long-trichome accessions. Functional validation revealed that overexpression of GaCPR5 increased long trichome abundance, and GaCPR5 localized to the nuclear periphery/nucleus, where it physically interacts with the cyclin-dependent kinase inhibitor GaSMR3. Moreover, silencing GaSMR3 significantly suppressed long trichome formation and altered cell cycle progression. In summary, this dissertation systematically elucidates parts of the genetic basis underlying cotton fiber-related traits and long trichome development from three levels: genetic mapping, gene family evolution, and molecular regulatory networks. We established a regulatory module of GaHDG11/GaHD1–GaZHD2–GaCPR5, GaSMR3, revealing that natural promoter variation, transcriptional regulation, and cell-cycle control collectively determine cotton trichome elongation. These findings provide novel insights into the specialized development of cotton epidermal cells and offer important genetic resources and theoretical foundations for cotton fiber quality improvement and stress-resistant breeding.
