ATP-binding cassette transporter G (ABCG) has been shown to be engaged in export of broad-spectrum compounds with structural differences, but little is known concerning its role in cutin formation of cotton (Gossypium spp.). In this study, we conduct a genome-wide survey and detected 69, 71, 124 and 131 ABCG genes within G. arboretum, G. raimondii, G. hirsutum and G. barbadense, separately. The above ABCGs could be divided into four groups (Ia, Ib, Ic, II). Some ABCG genes such as GhABCG15, whose homologous gene transports cuticular lipid in Arabidopsis, was preferentially expressed in the development of fiber. A weighted gene co-expression network analysis (WGCNA) demonstrated that GhABCG expression was significantly associated with the amount of 16-Hydroxypalmitate (a main component of cutin precursor) in cotton fibers. Further, silencing of GhABCG15 by virus-induced gene silencing (VIGS) in cotton generated brightened and crinkled leaves as well as reduced thickness of cuticle and increased permeability. Chemical composition analysis showed the cutin content in GhABCG15-silenced leaves had decreased while the wax content had increased. Our results provide an insight for better understanding of the role of the Gossypium ABCG family and revealed the essential role of GhABCGs in cotton cutin formation.

The SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family, a group of plant-specific transcription factors, plays a key role in plant growth and development through complex regulatory networks. Within this family, SPL9 has been identified as a key regulator of diverse biological processes. In this review, we summarize the current knowledge on SPL9, focusing on its expression regulatory mechanisms and roles in plant development, such as morphogenesis, reproductive processes, and crop yield determinations. We further describe its role in plant responses to abiotic and biotic stresses and its integration into broader regulatory networks. We also outline future research priorities and discuss potential applications of SPL9-based strategies in molecular design breeding to increase crop productivity and stress resistance.