The cotton ATP synthase δ1 subunit is required to maintain a higher ATP/ADP ratio that facilitates rapid fibre cell elongation.

The δ subunit of mitochondrial ATP synthase serves as a linker between the F(0) and F(1) sectors. Here, through microarray and quantitative RT-PCR, we found that the δ1 subunit was significantly up-regulated during cotton fibre cell elongation. Both the relative level and duration of GhATPδ1 transcripts correlated positively with the final length of different cotton germplasms. Elongating fibre cells had a significantly elevated ATP/ADP ratio, suggesting that a higher energy input is probably required for primary fibre cell wall formation and elongation. We obtained a putative full-length GhATPδ1 cDNA that shows 37% sequence identity to the Saccharomyces cerevisiae ATP16 at the deduced amino acid level. An almost wild-type growth rate was restored in atp16Δ cells that expressed GhATPδ1, with a resultant ATP/ADP ratio similar to that found in wild-type cells, indicating that the cotton gene was functional in yeast. Mitochondria prepared from 10 dpa wild-type fibre cells showed significantly higher ATP synthase activity in comparison to ovule samples from wild type and leaf samples. Exogenous application of piceatannol (PA) or oligomycin (OM), inhibitors of ATP synthase F(1) or F(0) subunits, respectively, in ovule culture media resulted in much shorter fibre cells and a significantly lower ATP/ADP ratio. Our data suggest that GhATPδ1 is important for activity of mitochondrial ATP synthase and is probably related to cotton fibre elongation.