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Title: The loss-of-function GLABROUS 3 mutation in cucumber is due to LTR-retrotransposon insertion in a class IV HD-ZIP transcription factor gene CsGL3 that is epistatic over CsGL1

Author
item PAN, YUPENG - University Of Wisconsin
item BO, KAILIANG - University Of Wisconsin
item CHENG, ZHIHUI - Northwest Agricultural & Forestry University
item Weng, Yiqun

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2015
Publication Date: 12/29/2015
Publication URL: http://handle.nal.usda.gov/10113/62226
Citation: Pan, Y., Bo, K., Cheng, Z., Weng, Y. 2015. The loss-of-function GLABROUS 3 mutation in cucumber is due to LTR-retrotransposon insertion in a class IV HD-ZIP transcription factor gene CsGL3 that is epistatic over CsGL1. Biomed Central (BMC) Plant Biology. 15(1):302. doi: 10.1186/s12870-015-0693-0.

Interpretive Summary: Trichomes developed from the protodermal cells (the outermost cell layer of the embryo) are hair-like structures covering the aerial parts of plants. Trichomes are of adaptive roles in evolution. The presence or absence of trichomes also constitutes an important quality issue for the end products of many specialty crops such as cucumber, Cucumis sativus L. In this study, we reported characterization and map-based cloning of a new trichome mutant, CUCUMBER GLABROUS 3 (csgl3) that may provide new knowledge on genetic control of trichome development in cucumber. The new trichome mutant RIL-46M exhibited completely glabrous phenotype on all aerial organs. Genetic analysis indicated that the glabrous phenotype was inherited as a single recessive gene, which was designated as csgl3. Fine genetic mapping delimited the csgl3 locus into a 68.4 kb genomic DNA region with 12 predicted genes. Evidence from genetic analysis, sequence alignment and allelic variations in natural populations suggested that the Arabidopsis PROTODERMAL FACTOR2 (PDF2)-Like gene (Csa6G514870) was the only candidate gene for CsGL3, which was 5,188 bp in length with 10 predicted exons. Gene expression analysis revealed loss-of-function of CsGL3 in the mutant which was due to the insertion of a long terminal repeat (LTR) retrotransposon in the fourth exon of CsGL3. CsGL3 encoded a class IV homeodomain-associated leucine zipper (HD-ZIP) protein contain a homeodomain and the START domain, and showed 70.7% amino acid sequence identity to Arabidopsis PDF2. Linkage analysis in segregation population and gene expression analysis of the CsGL1 and CsGL3 genes in csgl1, csgl3, and csgl1+3 genetic backgrounds uncovered interactions between the two genes. Phylogenetic analysis among 28 class IV HD-ZIP protein sequences from five species placed cucumber CsGL3 into the same clad with seven other members that play important roles in trichome initiation. Findings from the present study provide new insights into genetic control of trichome development in cucumber.

Technical Abstract: Trichomes developed from the protodermal cells are hair-like structures covering the aerial parts of plants. Trichomes are of adaptive roles in evolution. The presence or absence of trichomes also constitutes an important quality issue for cucumber. In this study, we reported characterization and map-based cloning of a new trichome mutant, CUCUMBER GLABROUS 3 (csgl3), which exhibited completely glabrous phenotype on all aerial organs. Genetic analysis indicated that the glabrous phenotype was inherited as a single recessive gene, which was designated as csgl3. Fine genetic mapping delimited the csgl3 locus into a 68.4 kb genomic DNA region with 12 predicted genes. Evidence from genetic analysis, sequence alignment and allelic variations in natural populations suggested that the Arabidopsis PDF2-like gene was the only candidate gene for CsGL3, which was 5,188 bp in length with 10 predicted exons. Gene expression analysis revealed loss-of-function of CsGL3 in the mutant which was due to the insertion of a long terminal repeat retrotransposon in the fourth exon. Linkage analysis in segregation population and gene expression analysis of the CsGL1 and CsGL3 genes in csgl1, csgl3, and csgl1+3 genetic backgrounds revealed interactions between the two genes. Phylogenetic analysis among 28 class IV HD-ZIP protein sequences from five species placed cucumber CsGL3 into the same clad with seven other members that play important roles in trichome initiation. Findings from the present study provide new insights into genetic control of trichome development in cucumber.