Alternative oxidase (AOX) over-expression improves cell expansion and elongation in cotton seedling exposed to cool temperatures.

KEY MESSAGE: Evidence that supports a relation between AOX expression and improvement in plant height, internode length, and total leaf area under cool temperature is shown. Cell expansion and elongation appear to be enhanced when AOX expression was increased. Cotton growth is sensitive to cool temperature during germination and early seedling development. Delayed emergence, seedling damage, and increased risk to disease are common. Late seasonal cool weather is a major factor limiting the consistent production of high-quality cotton lint in West Texas. Alternative oxidase functions in the inner membrane of the mitochondria via an alternative respiration pathway and serves as a multifunctional system for amelioration of abiotic and biotic stresses. Cotton seedling emergence and growth exposed to cool temperatures was examined in plants with enhanced AOX expression. Thirteen T1 seed lines showed 3 to 1 segregation for the T-DNA containing the tobacco AOX1 gene. Two over-expressing, single-copy, homozygous AOX lines (94-20T and 66-6T) and Null line (94-3N) were selected for examination. The transcript levels were ≈ 2 to 6 fold higher in the AOX lines compared to those of the Null line and wild-type in stem, leaf, root and boll tissues. The research examined the hypothesis that transgenic cotton with enhanced AOX expression will have enhanced growth traits under suboptimal cool temperatures. Improved plant height, internode length, plant height and internode length from second node, and total leaf area under cool temperatures were observed in AOX over-expression lines. This may be attributed to improved cell expansion and elongation characteristics in the AOX line.

A 3347-locus genetic recombination map of sequence-tagged sites reveals features of genome organization, transmission and evolution of cotton (Gossypium).

We report genetic maps for diploid (D) and tetraploid (AtDt) Gossypium genomes composed of sequence-tagged sites (STS) that foster structural, functional, and evolutionary genomic studies. The maps include, respectively, 2584 loci at 1.72-cM ( approximately 600 kb) intervals based on 2007 probes (AtDt) and 763 loci at 1.96-cM ( approximately 500 kb) intervals detected by 662 probes (D). Both diploid and tetraploid cottons exhibit negative crossover interference; i.e., double recombinants are unexpectedly abundant. We found no major structural changes between Dt and D chromosomes, but confirmed two reciprocal translocations between At chromosomes and several inversions. Concentrations of probes in corresponding regions of the various genomes may represent centromeres, while genome-specific concentrations may represent heterochromatin. Locus duplication patterns reveal all 13 expected homeologous chromosome sets and lend new support to the possibility that a more ancient polyploidization event may have predated the A-D divergence of 6-11 million years ago. Identification of SSRs within 312 RFLP sequences plus direct mapping of 124 SSRs and exploration for CAPS and SNPs illustrate the "portability" of these STS loci across populations and detection systems useful for marker-assisted improvement of the world's leading fiber crop. These data provide new insights into polyploid evolution and represent a foundation for assembly of a finished sequence of the cotton genome.