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CHARACTERIZATION OF A QTL AND CANDIDATE GENE (LSGA2OX2) ASSOCIATED WITH DARK INHIBITION OF LETTUCE SEED GERMINATION, Mohan Niroula

Mon Sep 11, 2017
4:15 PM - 4:30 PM
Cypress 1&2, MPH

Description

CHARACTERIZATION OF A QTL AND CANDIDATE GENE (LSGA2OX2) ASSOCIATED WITH DARK INHIBITION OF LETTUCE SEED GERMINATION

 

Niroula, M.1, Huo, H.1,2, Still, D.4, You, Y.S.4, Wei, S.5, Truco, M.3, Michelmore, R.W.1,3 and Bradford, K.J.1

1Department of Plant Sciences, Seed Biotechnology Center, University of California, Davis, Davis, California, USA

2Mid-Florida Research and Education Center, University of Florida, Apopka, FL USA

3Department of Plant Sciences and Genome Center, University of California, Davis, Davis, California, USA

4Department of Plant Sciences, California State University, Pomona, CA 91768, USA

5Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China

Contact: Mohan Niroula, mniroula@ucdavis.edu

 

Promotion of germination in lettuce and Arabidopsis seeds by light is associated with activation of gibberellin (GA) biosynthesis. We used a Recombinant Inbred Line ( RIL) population derived from a lettuce cultivar (Lactuca sativa cv. Salinas) that does not require light to germinate and a light-requiring accession of L. serriola (US96UC23) to map a quantitative trait locus (QTL) for the inhibition of lettuce seed germination by darkness. The same QTL was mapped to chromosome 7 in two independent mapping experiments using F6 and F9 generations of RIL seeds harvested from different locations (California, USA and Chile, respectively). A GA catabolic gene (LsGA2ox2) located within this QTL from both Salinas (Sal) and US96UC23 (UC) contained identical deduced protein sequences, but twelve single-nucleotide polymorphisms (SNPs) were identified in 1.4 kb of LsGA2ox2 promoter nucleotide sequences from the two lettuce genotypes, and 9 of these SNPs were clustered in a 93 bp region. Expression analyses revealed that LsGA2ox2 transcripts remained at a high level in non-germinated UC96US23 seeds imbibed for 24 h in the dark, while its expression substantially decreased in Salinas seeds imbibed in the dark and in imbibed seeds of both genotypes in the light. Complementation of an Arabidopsis atga2ox2 mutant line with ProUCGA2ox2::UCGA2ox2 and ProUCGA2ox2::SalGA2ox2 or expression of ProUCGA2ox2::UCGA2ox2 in Salinas lines resulted in strong inhibition of seed germination in the dark. By contrast, RNAi silencing of LsGA2ox2 in US96UC23 lines resulted in enhanced seed germination in the dark. Site-directed mutagenesis of three SNPs in the 93 bp window of the UC promoter resulted in failure to complement atga2ox2 mutants, suggesting that these SNPs are critical for upregulation of LsGA2ox2 in seeds imbibed in the dark. Furthermore, sequence analysis of LsGA2ox2 and its promoter region from cv. Grand Rapids (L. sativa, light-requiring) and W48 (L. serriola, not light-requiring) lines showed that all 9 SNPs in the 93 bp promoter region are conserved among either light-sensitive or light-insensitive genotypes, regardless of species. The combination of genetic mapping, mutant complementation, and conserved SNPs implicates degradation of GA by LsGA2ox2 in the inhibition of germination by darkness.


Speaker:

 
Mohan Niroula
UC Davis

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