Two investigations, one of the inheritance of stomatal regulation and its relation to heat tolerance and the other of seed gossypol content in Gossvpium barbadense, began yielding results in 1992. Mode of gene action conferring stomatal conductance varied with the parentage of crosses. Selective advance for high conductance appeared to be feasible in wide crosses, but limited in crosses of elite Pima strains. Variability for seed gossypol content in G. barbadense was surprisingly high. There was evidence of geographic and taxonomic structure to the variability observed. A conversion program to convert photoperiodic short-day flowering accession's of the G. barbadense germplasm collection to day neutrality continued.

Five experimental strains and Pima S-6 were grown in nine Regional Tests across the Pima belt in 1987. Experimental strain P70 averaged highest in yield both below and above 2,500 foot elevation. The difference in yield between Pima S-6 and P70 across all locations was 48 pounds of lint per acre. Sequential harvests at Phoenix and Safford, AZ, indicated that P70 was the earliest and Pima S-6 the latest entry in the 1987 Regional Test.

Seed increase of 104 accessions and data collection on 65 accessions were obtained in 1988 to further the maintenance and evaluation of the Gossypium barbadense L. germplasm collection. In a program of conversion of tropical non flowering cottons to a day-neutral flowering habit, 63 accessions were advanced 1 generation by backcross. A systematic screening of the G. barbadense collection for bacterial blight resistance involving 200 accessions from 21 countries yielded 8 accessions resistant to races 1, 2, 7, and 18 of the pathogen. Genetic inheritance and linkage investigations of a male sterile and a foliar mutant progressed. An investigation of the geographic and taxonomic distribution of the ovate leaf trait was concluded with negative results. The frequency of the 2 mutant genes ov₁ and ov₂ proved to be too rare to yield meaningful taxonomic or geographic information about the species. Preliminary results from a performance evaluation of interspecific hybrid cottons conducted at Maricopa and Safford AZ, indicated strong environmental influences on hybrids, but generally favorable yield earliness and plant height data were obtained from the higher -elevation Safford location.

A cotton PATE cDNA clone has a 1.7-kb insert with an coding region for 410 amino acids, lacking codons for the three N-terminal amino acids. The predicted amino acid sequence of the PATE preprotein has a characteristic stromal-targeting domain and a 63% identity to the Arabidopsis FatB1 thioesterase sequence. A cotton genomic clone containing a 17.4-kb DNA segment was found to encompass a palmitoyl-ACP thioesterase (FatB1) gene. The gene spans 3.6 kb with six exons and five introns. The six exons are identical in nucleotide sequence to the open reading frame of the corresponding cDNA, and would encode a preprotein of 413 amino acids. The preprotein is identified as a FatB thioesterase from its deduced amino acid sequence similarity to those of other FatB thioesterase preproteins. A 5'-flanking region of 914 bp was sequenced, with the potential promoter/enhancer elements including basic helix-loop-helix elements (E box). Alkaline blot hybridization of cotton genomic DNA suggests the presence at least two FatB1 thioesterase genes in cotton. Four plasmid constructs for both constitutive and seed-specific anti-sense RNA suppression and gene-transgene co- suppression of PATE gene expression were successfully generated. Two overlapping cotton genomic clones were found to encompass a Δ-12 fatty acid desaturase (FAD2-3) gene. The continuous FAD2-3 coding region is 1,155 bp and would encode a protein of 384 amino acids. The FAD2-3 gene has one large intron of 2,967 bp entirely within its 5'-untranslated region. Several potential promoter/enhancer elements, including several light responsive motifs occur in the 5'-flanking region. Yeast cells transformed with a plasmid construct containing the cotton FAD2-3 coding region accumulate an appreciable amount of linoleic acid (18:2), not normally present in wild-type yeast cells, indicating that the gene encodes a functional FAD2 enzyme.

The lipid composition of cotton (Gossypium hirsutum, L) fibers was determined. Fatty acid profiles revealed that linolenate and palmitate were the most abundant fatty acids present in fiber cells. Phosphatidylcholine was the predominant lipid class in fiber cells, while phosphatidylethanolamine, phosphatidylinositol and digalactosyldiacylglycerol were also prevalent. An unusually high amount of phosphatidic acid was observed in frozen cotton fibers. Phospholipase D activity assays revealed that this enzyme readily hydrolyzed radioactive phosphatidylcholine into phosphatidic acid. A profile of expressed sequence tags (ESTs) for genes involved in lipid metabolism in cotton fibers was also obtained. This EST profile along with our lipid metabolite data was used to predict lipid metabolic pathways in cotton fiber cells.

The chromosomes involved in twenty reciprocal translocations in G. hirsutum were reidentified by means of a specially designed crossing program. Each translocation line was crossed to appropriate monosomic, monotelodisomic, and/or translocation lines. The F₁ hybrids were then scored cytologically to verify the original chromosome identification. These twenty reciprocal translocations now become the cytogenetic tester set for G. hirsutum. Seed stocks for each verified translocation line will be maintained at, and distributed by, the University of Arizona. Nineteen of the twenty heterozygous translocations had a modal chiasma frequency per quadrivalent of four. Fourteen of these translocation lines formed predominantly ring multivalents at MI, and the remaining five translocations usually formed multivalents with at least one interstitial chiasma. One translocation line, which was originally produced by an interspecies cross, formed predominantly chains at MI. This increased amount of chaining in the quadrivalent is probably the result of interspecific chromosome material within the translocation reducing the chiasma frequency. The orientation of the centromeres in quadrivalents is influenced by the size of the chromosomes involved in the reciprocal translocation, and the constraints imposed by the chiasmata within the chromosome arms. Ten of the twenty reciprocal translocations studied formed predominantly alternate orientations at MI. Eight of these ten translocation lines were reciprocal translocations between two A subgenome chromosomes. This suggests that the large A subgenome chromosomes allow the quadrivalent to be more flexible, resulting in easy reorientation to the stable alternate configuration. Proximal chiasma formation influences the orientation and probable involvement of the homologous centromeres in spindle formation. Lines in which a high frequency of multivalents with interstitial chiasma were observed had a significantly lower frequency of multivalents with either one or two centromeres not involved in spindle formation of 3:1 orientations. In most of the heterozygous translocations, identification of each chromosome within the quadrivalent at MI was not possible. Estimation formulae were developed to estimate the positions of the breakpoints and the genetic lengths of each segment defined by multivalents in these translocations.

Plant architecture is an important agronomic trait driven by meristematic activities. Indeterminate meristems set repeating phytomers while determinate meristems produce terminal structures. The centroradialis/terminal flower1/self pruning (CETS) gene family modulates architecture by controlling determinate and indeterminate growth. Cotton (G. hirsutum) is naturally a photoperiodic perennial cultivated as a day-neutral annual. Management of this fiber crop is complicated by continued vegetative growth and asynchronous fruit set. Here, cotton CETS genes are phylogenetically and functionally characterized. We identified eight CETS genes in diploid cotton (G. raimondii and G. arboreum) and sixteen in tetraploid G. hirsutum that grouped within the three generally accepted CETS clades: flowering locus T (FT)-like, terminal flower1/self pruning (TFL1/SP)-like, and mother of FT and TFL1 (MFT)-like. Over-expression of single flower truss (GhSFT), the ortholog to Arabidopsis FT, accelerates the onset of flowering in Arabidopsis Col-0. In mutant rescue analysis, this gene driven by its native promoter rescues the ft-10 late flowering phenotype. GhSFT upstream sequence was used to drive expression of the uidA reporter gene. As anticipated, GUS accumulated in the vasculature of Arabidopsis leaves. Cotton has five TFL1-like genes, all of which delay flowering when ectopically expressed in Arabidopsis; the strongest phenotypes fail to produce functional flowers. Three of these genes, GhSP, GhTFL1-L2, and GhBFT-L2, rescue the early flowering tfl1-14 mutant phenotype. GhSPpro:uidA promoted GUS activity specifically in plant meristems; whereas, other GhTFL1-like promoters predominately drove GUS activities in plant vascular tissues. Finally, analysis of Gossypium CETS promoter sequences predicted that GhSFT, GhSP, GhTFL1-L1, GhTFL1-L2 and GhBFT-L2 are regulated by transcription factors involved in shoot and flowering development. Analysis of cotton's two MFT homologs indicated that neither gene functions to control shoot architecture. Our results emphasize the functional conservation of members of this gene family in flowering plants and also suggest this family as targets during artificial selection of domestication.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.