Functions of phytosterols in seed development of upland cotton (Gossypium hirsutum L.)

Abstract Cotton seeds are important for the yield of fiber, oil, and protein. Previous studies have shown that phytosterols play important roles in fiber growth. However, the functions of phytosterols in cotton seed development remain to be elucidated. In this study, we detected the phytosterol content of cotton seeds at various developmental stages by gas chromatography–mass spectrometry (GC–MS). We found that the contents of sitosterol and campesterol were higher in the stages from 5 to 25 days post-anthesis (DPA) and decreased rapidly after 25 DPA. Moreover, the ratio of campesterol to sitosterol was low before 15 DPA and high at 20 and 25 DPA. During the early developmental stages of cotton seeds, sitosterol and campesterol are the predominant phytosterols, and the sitosterol content is much higher than that of campesterol. In addition, we found that most phytosterol biosynthetic genes were highly expressed in 10-DPA and/or 20-DPA seeds by qRT-PCR, which was consistent with the phytosterol content in cotton seeds. When the cotton bud was treated with the sterol biosynthesis inhibitors tridemorph and fenpropimorph, the growth of cotton seeds was retarded. Moreover, overexpression of the phytosterol biosynthetic gene GhSMT2−1 significantly increased the size and weight of cotton seeds. These results indicate that phytosterols indeed participate in the regulation of cotton seed development.