Wang_2025_Theor.Appl.Genet_138_126

A fiber micronaire QTL qMIC-A11 was fine-mapped, and the GDSL esterase/lipase gene GbGELP was identified as the causal gene of the QTL. GbGELP modulates cell elongation and cotton fiber development. Fine mapping and map-based cloning of fiber micronaire (MIC)-related quantitative trait loci (QTL) have not been reported to date. Here, we utilized a G. hirsutum (Gh) acc. TM-1-G. barbadense (Gb) acc. Hai7124 introgression line CSSL47, which exhibits a significant decrease in MIC compared to TM-1, to cross with TM-1 and develop the F(2) and F(2:3) secondary segregating populations. Further, a stable MIC QTL qMIC-A11 was simultaneously detected in the F(2) and F(2:3) populations and anchored within a 407 kb region. Among them, GB_A11G1593 encoding a GDSL esterase/lipase, exhibited substantially higher expression levels at fiber elongation period in CSSL47 compared to TM-1, which was temporally identified as the causal gene for qMIC-A11 and named as GbGELP. The heterologous expression of GbGELP in Arabidopsis showed increased root length, root cell length, rosette leaf growth, and trichome density. However, knockdown of GbGELP homologs in CSSL47 significantly decreased the fiber length. Further investigation found that there was an A/T single-nucleotide polymorphism variation (SNP) in the promoter of GELP orthologs between CSSL47 and TM-1, which results in a differential CATTAAATT/CATTTAATT HAHR1-box cis-acting element, a binding site for the homeodomain-leucine zipper IV (HD-ZIP IV). GbGELP was regulated by a HD-ZIP IV transcription factor GhHDG2 via binding to the CATTAAATT element in the GbGELP promoter, while GhGELP could be activated due to GhHDG2 unable to bind the CATTTAATT element in the GhGELP promoter. The fine-mapped MIC QTL qMIC-A11, along with the causal gene GbGELP, will be utilized to improve the fiber quality in cotton breeding.