Cloning, expression and chromosome mapping of arabinogalactan protein gene in cotton.

The Ligon lintless mutant (Li1li1) is a fiber elongation developmental mutant with a dominant monogenetic mutation characterized by short fibers and distorted leaf,stem and flower growth,and the recessive pure line (li1li1) exhibits normal fiber developmental characteristics. The objectives of this study were to isolate genes preferentially or specifically expressed in fiber elongation stage by comparing gene expression differences between Li1li1 and li1li1. RNA isolated from 10 days post anthesis (DPA) fibers and ovules mixture in Li1li1 and li1li1 were used to screen differential gene expression in fiber development using differential display reverse transcriptase polymerase chain reaction (DDRT-PCR). One differential expression cDNA segment was isolated and the corresponding full-length cDNA was cloned by 5' RACE method. Sequencing and bioinformatics analysis showed the protein had 52% homology with arabinogalactan protein from Arobidopsis,therefore,this gene was temporarily des-ignated GhAGP. RT-PCR and quantitative real time RT-PCR assays all indicated that the transcript of GhAGP is constitutively expressed in root,stem,leaf and fiber,with higher expression levels in fiber cells as fiber developments. Genomic sequence analysis showed there was one copy of GhAGP in diploid cotton species,G. herbaceum and G. raimondii,and two copies in te-traploid cotton species,G. hirsutum and G. barbadense respectively,indicating that the sub-genome A and subgenome D contain each of them. Using the BC1 mapping population derived from the hybridization between the upland cotton standard line TM-1 and G. barbadense cultivar Hai7124,and TM-1 as recurrent parent,two copies of GhAGP were located on the homoelo-gous chromosomes 6 and 25,respectively.