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The monotonicity of color type in naturally colored cottons (NCCs) has become the main limiting factor to their widespread use, simultaneously coexisting with poor fiber quality. The synchronous improvement of fiber quality and color become more urgent and crucial as the demand for sustainable development increases. The homologous gene of wild cotton Gossypium stocksii LAC15 in G. hirsutum, GhLAC15, was also dominantly expressed in the developing fibers of brown cotton XC20 from 5 DPA (day post anthesis) to 25 DPA, especially at the secondary cell wall thickening stage (20 DPA and 25 DPA). In XC20 plants with downregulated GhLAC15 (GhLAC15i), a remarkable reduction in proanthocyanidins (PAs) and lignin contents was observed. Some of the key genes in the phenylpropane and flavonoid biosynthesis pathway were down‐regulated in GhLAC15i plants. Notably, the fiber length of GhLAC15i plants showed an obvious increase and the fiber color was lightened. Moreover, we found that the thickness of cotton fiber cell wall was decreased in GhLAC15i plants and the fiber surface became smoother compared to that of WT. Taken together, this study revealed that GhLAC15 played an important role in PAs and lignin biosynthesis in naturally colored cotton fibers. It might mediate fiber color and fiber quality by catalyzing PAs oxidation and lignin polymerization, ultimately regulating fiber colouration and development. [ABSTRACT FROM AUTHOR]

Lipid droplet-associated proteins (LDAPs) play essential roles in tissue growth and development and in drought stress responses in plants. Cotton is an important fiber and cash crop; however, the LDAP family has not been characterized in cotton. In this study, a total of 14, six, seven, and seven genes were confirmed as LDAP family members in Gossypium hirsutum , Gossypium raimondii , Gossypium arboreum , and Gossypium stocksii , respectively. Additionally, expansion in the LDAP family occurred with the formation of Gossypium , which is mirrored in the number of LDAPs found in five Malvaceae species ( Gossypioides kirkii , Bombax ceiba , Durio zibethinus , Theobroma cacao , and Corchorus capsularis ), Arabidopsis thaliana , and Carica papaya . The phylogenetic tree showed that the LDAP genes in cotton can be divided into three groups (I, II, and III). The analysis of gene structure and conserved domains showed that LDAPs derived from group I ( LDAP1 / 2 / 3 ) are highly conserved during evolution, while members from groups II and III had large variations in both domains and gene structures. The gene expression pattern analysis of LDAP genes showed that they are expressed not only in the reproductive organs (ovule) but also in vegetative organs (root, stem, and leaves). The expression level of two genes in group III, GhLDAP6_At/Dt , were significantly higher in fiber development than in other tissues, indicating that it may be an important regulator of cotton fiber development. In group III, GhLDAP2_At / Dt , especially GhLDAP2_Dt was strongly induced by various abiotic stresses. Decreasing the expression of GhLDAP2_Dt in cotton via virus-induced gene silencing increased the drought sensitivity, and the over-expression of GhLDAP2_Dt led to increased tolerance to mannitol-simulated osmotic stress at the germination stage. Thus, we conclude that GhLDAP2_Dt plays a positive role in drought tolerance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Zhao, Duan, Liu, Wu, Yu, Ke, Cai, Mei, Zhu and Sun.)

As water-soluble, natural pigments, anthocyanins are responsible for the red, purple and blue colors of many flowers, which attract pollinators to spread pollen. The colors of flowers are also essential for plants to survive in the nature and become one of the most significant characteristics of ornamental plants. In the booming floriculture industry, to produce various flower colors could increase the richness of natural colors, but it is still difficult to breed flowers with coveted blue color. The diversity of flower color is mainly determined by the types and contents of anthocyanins and their derivatives. The synthesis of delphinidin pigments is the key factor for breeding blue flowers. However, there are no structural genes in many plants to biosynthesize delphinidin pigments. Blue flowers are successfully created by genetic engineering in recent years. In this paper, using common ornamental plants as examples, we review the mechanism of plant flower coloration from the aspects of the key factors affecting the synthesis of delphinidin pigment and the production strategies of blue flowers based on the regulation of anthocyanin metabolism. Different strategies of molecular breeding could provide opportunities to improve colors of other floriculture plants and to develop anthocyanin-rich economic crops, such as colored cotton with blue fibers.