Progress 10/01/00 to 09/30/06
Outputs
Chloroplast DNA and nuclear sequencing analysis of cultivated and citron type watermelon accessions, collected from many different geographical areas around the world, was conducted to infer their evolutionary relationships, origin and domestication events. Variability among cultivated watermelon was limited even at nuclear regions, while variability among citron type accessions suggests a center of diversity in southern Africa. The cultivated and wild watermelon appear to have diverged independently from a common ancestor, probably C. ecirrhosus from Namibia. Drought induced gene expression was studied in Citrullus colocynthis, a drought tolerant perennial species with a deep root system distributed in the African desert. cDNA-AFLP and real-time quantitative relative PCR techniques were used to study gene expression in roots and shoots of plants exposed to drought stress. Several genes with similarity to known function genes involved in transport facilitation,
metabolism and energy and stress related proteins were induced. These results suggest a complex adaptive process in response to drought stress.
Impacts
Domestication of watermelon involved manipulation of several key loci related to fruit size, shape, color and taste. Understanding the process of domestication of watermelon and colonization all over the world is fundamental to the study of its evolutionary diversification. DNA sequence analysis of sections of the chloroplast genome of wild and cultivated Citrullus species, collected all over the world, identified several polymorphisms which could be used to uncover their evolutionary relationships and domestication patterns of the cultivated watermelon. Watermelon and citron type diverged independently from a common ancestor, probably C. ecirrhosus from Namibia. Very little diversity was detected among watermelon accessions.
Publications
- Dane, F., and J. Liu. 2006. Diversity and origin of cultivated and citron type watermelon (Citrullus lanatus). Genetic Resources and Crop Evolution (on line 10.1007/s10722-006-9107-3).
- Dane, F., J. Liu and C. Zhang. 2006. Phylogeography of the bitter apple: Citrullus colocynthis. Genetic Resources and Crop Evolution on line (10.1007/s10722-005-4897-2).
- Si, Y., and F. Dane. 2006. Drought-induced gene expression in roots of Citrullus colocynthis. Cucurbitaceae 2006: 48-50.
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Progress 01/01/05 to 12/31/05
Outputs
Cultivated and wild (citron type) watermelon collected from different areas on the African continent were investigated using DNA sequence analysis of several non-coding chloroplast and nuclear regions. Distinct chlorotype lineages were identified separating the cultivated watermelon from var. citroides accessions, suggesting an ancient split from a common ancestor and haplotype fixation. At least three haplotypes were detected within var. citroides. Accessions with the most ancient haplotype originated in Swaziland and South Africa. C. colocynthis, native to the desert regions of Africa and known for its extreme levels of drought tolerance, has been chosen as a model species to study gene expression under water deficit stress. Differential expression of genes in this species were investigated using cDNA-AFLP. Several genes implicated in protein repair, RNA binding and plant defense showed differential expression under drought stress conditions.
Impacts
Understanding key loci involved in the domestication syndrome of watermelon, related to fruit size, shape, color and taste, will provide tools for genetic improvement of watermelon. Drought limits the growth and productivity of watermelon production in Alabama. Knowledge of the expression of genes related to drought stress in Citrullus colocynthis, known for its extreme levels of drought tolerance, will improve our understanding of mechanisms involved in domesticated watermelon.
Publications
- Liu, J. 2005. Phylogeny an biogeography of watermelon [Citrullus lanatus (Thunb). Matsum & Nakai] based on chloroplast, nuclear sequence and AFLP marker data. MS Thesis, Auburn University, Auburn, AL 36849.
- Zhang, C., P. Lang, F. Dane, R.C. Ebel, N.K. Singh, R. Locy and W.A. Dozier. 2005. Cold acclimation induced genes of trifoliate orange (Poncirus trifoliata). Plant Cell Reports: 23: 764-769
- Zhang, C., P. Lang, R.C. Ebel, F. Dane, N.K. Singh, R. Locy and W.A. Dozier. 2005. Down-regulated gene expression of cold acclimated Poncirus trifoliata. Canadian Journal of Plant Science 85: 417-424
- Lang, P, C. Zhang, R.C. Ebel, F. Dane, and W. A. Dozier. 2005. Identification of cold acclimated genes in leaves of Citrus unshiu by mRNA differential display. Gene 356: (available on line as GENE-35089).
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Progress 01/01/04 to 12/31/04
Outputs
Chloroplast and single-copy nuclear DNA investigations in accessions of wild and cultivated Citrullus species from different geographical areas were continued to gain a better understanding of the evolution of species in the genus and molecular events associated with the domestication of cultivated watermelon. Variability within Citrullus at chloroplast DNA was detected primarily at non-coding regions of high A+T content. Variability observed at the nuclear region (G3pdH intron 2) revealed higher but similar patterns of differentiation. Biogeographic patterns detected within C. colocynthis point to separate colonization events from Africa into Asia. The cultivated watermelon diverged relatively recently ( 1 MYA) from a drought resistant species from Namibia. cDNA-AFLP was used to study differential gene expression in drought resistant C. colocynthis to gain insights into the molecular mechanisms of drought resistance to improve the stress tolerance of commercial
watermelon. Several up and down-regulated genes were identified.
Impacts
Sequence analysis of chloroplast and nuclear DNA regions makes it possible to infer evolutionary relationships in the genus Citrullus. The goal is to determine key loci involved in the domestication syndrome, related to fruit size, shape, color and taste. A precise knowledge of the phylogeography of watermelon will provide tools for genetic improvement of this economically important crop.
Publications
- Dane, F., and P. Lang. 2004. Sequence variation at cpDNA regions of watermelon and related wild species: implications for the evolution of Citrullus haplotypes. American Journal of Botany 91: 1922-1929.
- Dane, F., P. Lang and R. Bakhtiyarova. 2004. Comparative analysis of chloroplast DNA variability in wild and cultivated Citrullus species. Theoretical and Applied Genetics 108: 958-966.
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Progress 01/01/03 to 12/31/03
Outputs
Comprehensive map development of the watermelon genome was continued with emphasis on AFLP markers linked to disease resistance and domestication traits. Chloroplast DNA investigations in accessions of wild and cultivated Citrullus species from different geographical areas were continued to gain an understanding of the evolution of species in the genus and molecular events associated with the domestication of cultivated watermelon. Universal cpDNA primers were chosen for sequence analysis upon the discovery of phylogenetically informative restriction enzyme site differences within Citrullus species. Several informative regions were sequenced. Most of the cpDNA characters (96%) were invariant with 2.6% parsimony-uninformative and 1.1% parsimony informative characters. Mitochondrial DNA sequencing (at nad) was also conducted, but abandoned because of lack of variant sites among Citrullus species. Based on chloroplast sequence information, the cultivated watermelon
diverged relatively recently ( 1 MYA) from C. ecirrhosus, a drought resistant species from Namibia. Biogeographic patterns detected within C. colocynthis point to separate colonization events from the Middle East into Africa.
Impacts
Development of a detailed linkage map of watermelon will make it possible to locate and manipulate individual factors associated with many complex traits such as disease resistance and fruit quality. The intent is to determine key loci involved in the domestication syndrome, all related to fruit size, shape, color and taste.
Publications
- Dane, F., and R. Bakhtiyarova. 2003. Diagnostic chloroplast DNA haplotypes to distinguish cultivated from citron type watermelon. Cucurbit Genetic Cooperative 23
- Dane, F., and P. Lang. 2003. Phylogenetic relationships of Citrullus (Cucurbitaceae) using DNA sequences from several coding and noncoding chloroplast DNA regions: implications for evolution of watermelon. Botany 2003, Annual Meeting of the Botanical Society of America, p 53.
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Progress 01/01/02 to 12/31/02
Outputs
Experiments to develop a comprehensive linkage map of the watermelon genome with emphasis on markers linked to disease resistance genes and horticulturally important domestication traits were continued. Mapping was conducted in an F2 population segregating for gummy stem blight resistance using an efficient PCR-based method called amplified polymorphic DNA (AFLP). Specific restriction enzyme combinations (PstI/MseI) and fluorescently labeled primers were used to detect AFLP products. The reliability and reproducibility of the technique was tested. More than 40 different primer combinations were used and a large percentage of those gave reliable and reproducible results and will be used in the mapping population. Chloroplast DNA investigations were conducted in Citrullus lanatus (cultivated watermelon variety lanatus and wild citron variety citroides) and closely related Citrullus species (C. colocynthis, C. ecirrhosus, and C. rehmii) to investigate the evolution of
species in the genus and trace the domestication of watermelon from its wild relatives. More than 20 different primer pairs were used to detect polymorphisms in the cucurbit chloroplast genome. These studies have uncovered a small number of variable regions, which provide intra and interspecific differences and species diagnostic patterns that are being used to deduce evolutionary patterns related to domestication of watermelon from its wild relatives.
Impacts
Fruit size, shape and color are major factors determining yield, quality and consumer acceptability in watermelon. Fruit shape and size are difficult to approach with the tools of molecular biology. If more is known about the evolution and domestication of watermelon, then the identity of genes which account for the transition from wild forms bearing small bitter fruit to cultivars with large variably shaped sweet fruit associated with modern horticulture can be studied and isolated.
Publications
- Dane, F. 2002. Chloroplast DNA investigations in Citrullus using PCR-RFLP analysis. Cucurbitaceae 2002: 100-108.
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Progress 01/01/01 to 12/31/01
Outputs
In order to develop a detailed linkage map of watermelon, research was conducted to identify informative molecular markers using primers derived from expressed sequence tags (ESTs) of known watermelon genes. To discover polymorphism, products amplified using DNA from cultivated and wild watermelon were digested with a collection of restriction enzymes. The success rate for converting cDNA sequences into polymorphic sequence-tagged sites (STS) was low, however. Only a few polymorphic STS could be identified. Research focus will be shifted towards use of amplified fragment length polymorphic (AFLP) markers and retrotransposon derived markers.
Impacts
Wild and domesticated watermelons are dramatically different in fruit characteristics, insect and disease resistance. The lack of information on the genetic basis of these differences and their linkage relationships has slowed introgression of useful traits from wild germplasm. To date only a small rudimentary map is available for watermelon with a large RAPD cluster from the wild form, even though a high number of DNA sequences of genes of known function are available. It is our intent to use the DNA sequence information to gain a better understanding of the process of domestication in watermelon.
Publications
- No publications reported this period
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