Sucrose Synthase (SuSy) Gene Expression: An Indicator for Cotton Fiber Initiation and Early Development

Cotton (Gossypium hirsutum L.) fiber initiation from ovule epidermal cells happen from 0 to 5DPA, invertase (INV) and sucrose synthase (SuSy) are crucial for fiber initiation, cell expansion, and elongation. We used two commercial cotton varieties, Xuzhou 142-normal wild-type (WT) and Sea Island PimaS-4 (PimaS-4) as controls and compared with three fiber mutants, Xuzhou 142-fl (fl), Xuzhou 142-N (N) and Ligon lintless (Li). SuSy, INV activity, sugars and malate content were measured at fiber cell initiation and early development stage. Increased Susy activity was detected in WT, PimaS-4 and Li ovules at 0 DPA than the fiber mutant lines fl and N. On the other hand, fl mutant showed high sucrose contents than N and Li during 0 to 1 DPA. Nosignificant changes happen in studied cotton lines with respect to INV from 1 to 5 DPA altogether. There was a significant difference in total soluble sugars and malate contents between WT and fl cotton ovules at early elongation stage (5 DPA). The results revealed that SuSy activity at anthesis day indicates the fate of ovule epidermal cells to bulge out and form fiber initials. The reduced SuSy activity in fl ovules at 0DPA results in a lack of fiber cell initiation and lead to fiberless seed phenotype. The study will pave the way towards unraveling the mechanism of fiber initiation and development by exploring the role of different fiber-related genes.