Location: Crop Improvement and Protection ResearchTitle: LsGA2ox2 regulates lettuce seed germination under darkness Author
|Huo, Heqiang - University Of Florida|
|Niroula, Mohan - University Of California|
|Hill, Theresa - University Of California|
|Li, Juncheng - University Of Florida|
|Nguyen, Chi - University Of Florida|
|Truco, Maria Jose - University Of California|
|Michelmore, Richard - University Of California|
|Bradford, Kent - University Of California|
Submitted to: American Society of Horticulture Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/14/2018
Publication Date: 8/3/2018
Citation: Huo, H., Niroula, M., Hill, T., Li, J., Nguyen, C., Truco, M.J., Simko, I., Michelmore, R.W., Bradford, K. 2018. LsGA2ox2 regulates lettuce seed germination under darkness. American Society of Horticultural Science Annual Meeting, July 31-August 3, 2018, Washington, DC.
Technical Abstract: Lettuce seed germination is promoted by light through activation of gibberellin (GA) biosynthesis. A quantitative trait locus for inhibition of lettuce seed germination by the darkness was mapped to chromosome 7 using a RIL population derived from a dark-germinating cultivar (Lactuca sativa cv. Salinas) and a light-requiring accession of L. serriola (US96UC23). The LsGA2ox2 gene encoding a GA-inactivation enzyme was located in this QTL region and exhibited distinct expression patterns in ‘Salinas’ and US96UC23 seeds imbibed in the dark. Nine of twelve SNPs between ‘Salinas’ and US96UC23 (UC) were within a 93 bp window in the promoter of LsGA2ox2, and the same 9 SNPs were conserved in light-requiring ‘Grand Rapids’ (L. sativa) and dark-germinating W48 (L. serriola). Expression of ProUCGA2ox2::UCGA2ox2 in ‘Salinas’ lines resulted in strong inhibition of seed germination in the dark. Site-directed mutagenesis of three SNPs associated with an abscisic acid-responsive motif in the UCGA2ox2 promoter resulted in failure to complement atga2ox2 mutants, suggesting that these SNPs are critical for upregulation of LsGA2ox2 in seeds imbibed in the dark. Knockout of LsGA2ox2 through CRISPR/Cas9 in ‘Grand Rapids’ or RNAi silencing of LsGA2ox2 in US96UC23 resulted in stem elongation and enhanced seed germination in the dark that are associated GA upregulation. The combination of genetic mapping, mutant complementation, and conserved SNPs implicates degradation of GA by LsGA2ox2 in the inhibition of germination by darkness. Our results may facilitate breeding of lettuce varieties with more uniform germination of pelleted seeds and improve lettuce stand establishment and yield.