Identification of a delta-TIP cDNA clone and determination of related A and D genome subfamilies in Gossypium species.

Tonoplast intrinsic proteins (TIPs) have been implicated in the process of cell elongation, such as occurs in the developing cotton fiber. We have isolated a cDNA clone (997 bp in length) from a cotton (Gossypium hirsutum L.) library which putatively encodes a protein of 248 residues (Mr 25079) with 85% identity to Arabidopsis delta-TIP. The derived amino acid sequence included two conserved sequences associated with major intrinsic proteins (SGxHxNPA at residues 78 to 85, NPA residues at 197 to 199) and a cysteine residue at 116 which is reported to bind mercury in Arabidopsis delta-TIP. The polymerase chain reaction was used to generate partial genomic clones of the cotton delta-TIP. In comparison to other genomic TIP sequences, the number (two) and position of the introns were conserved in cotton. Comparing the TIP sequences from cotton revealed two subfamilies, which were consistently distinguished by a Tsp45I restriction site polymorphism. This polymorphism was used to demonstrate that TIP subfamilies were specific to either the A or D genomes of Gossypium. When delta-TIP DNA fragments were amplified from cDNA of fiber 14 days after anthesis, the A and D were found, indicating the presence of delta-TIP transcripts in these elongating cells.