Comparative Lipidomics Analysis Provides New Insights into the Metabolic Basis of Color Formation in Green Cotton Fiber

Green fiber (GF) is a naturally colored fiber. A limited understanding of its color formation mechanism restricts the improvement of colored cotton quality. This experiment used upland cotton green fiber germplasm 1-4560 and genetic inbred line TM-1; the lipid profiles of green fibers at 30 (white stage) and 35 days post-anthesis (DPA) (early greening stage), as well as those of TM-1 at the same stages, were revealed. Among the 109 differential types of lipids (DTLs) unique to GF, the content of phosphatidylserine PS (16:0_18:3) was significantly different at 30 and 35 DPA. It is speculated that this lipid is crucial for the pigment accumulation and color formation process of green fibers. The 197 DTLs unique to TM-1 may be involved in white fiber (WF) development. Among the shared DTLs in GF35 vs. GF30 and WF35 vs. WF30, sulfoquinovosyldiacyl-glycerol SQDG (18:1_18:1) displays a significant difference in the content change between green fibers and white fibers, potentially affecting color formation through changes in content. The enriched metabolic pathways in both comparison groups are relatively conserved. In the most significantly enriched glycerophospholipid metabolic pathway, 1-acyl-sn-glycero-3-phosphocholine (C04230) only appears in white cotton. This indicates differences in the metabolic pathways between white and green fibers, potentially related to different mechanisms of color formation and fiber development. These findings provide a new theoretical basis for studying cotton fiber development and offer important insights into the specific mechanism of green fiber color formation.