Original Paper

Theoretical and Applied Genetics

, Volume 122, Issue 1, pp 95-108

Open Access This content is freely available online to anyone, anywhere at any time.

A gene encoding an abscisic acid biosynthetic enzyme (LsNCED4) collocates with the high temperature germination locus Htg6.1 in lettuce (Lactuca sp.)

  • Jason ArgyrisAffiliated withDepartment of Plant Sciences, One Shields Ave, University of CaliforniaSyngenta Seeds S.A, Centro De Investigación Y Ensayos Finca los Sauras, Ctra de IFEPA
  • , María José TrucoAffiliated withGenome Center, One Shields Ave, University of California
  • , Oswaldo OchoaAffiliated withGenome Center, One Shields Ave, University of California
  • , Leah McHaleAffiliated withGenome Center, One Shields Ave, University of CaliforniaDepartment of Horticulture and Crop Science, The Ohio State University
  • , Peetambar DahalAffiliated withDepartment of Plant Sciences, One Shields Ave, University of California
  • , Allen Van DeynzeAffiliated withSeed Biotechnology Center, One Shields Ave, University of California
  • , Richard W. MichelmoreAffiliated withDepartment of Plant Sciences, One Shields Ave, University of CaliforniaGenome Center, One Shields Ave, University of California
  • , Kent J. BradfordAffiliated withDepartment of Plant Sciences, One Shields Ave, University of CaliforniaSeed Biotechnology Center, One Shields Ave, University of California Email author 

Abstract

Thermoinhibition, or failure of seeds to germinate when imbibed at warm temperatures, can be a significant problem in lettuce (Lactuca sativa L.) production. The reliability of stand establishment would be improved by increasing the ability of lettuce seeds to germinate at high temperatures. Genes encoding germination- or dormancy-related proteins were mapped in a recombinant inbred line population derived from a cross between L. sativa cv. Salinas and L. serriola accession UC96US23. This revealed several candidate genes that are located in the genomic regions containing quantitative trait loci (QTLs) associated with temperature and light requirements for germination. In particular, LsNCED4, a temperature-regulated gene in the biosynthetic pathway for abscisic acid (ABA), a germination inhibitor, mapped to the center of a previously detected QTL for high temperature germination (Htg6.1) from UC96US23. Three sets of sister BC3S2 near-isogenic lines (NILs) that were homozygous for the UC96US23 allele of LsNCED4 at Htg6.1 were developed by backcrossing to cv. Salinas and marker-assisted selection followed by selfing. The maximum temperature for germination of NIL seed lots with the UC96US23 allele at LsNCED4 was increased by 2–3°C when compared with sister NIL seed lots lacking the introgression. In addition, the expression of LsNCED4 was two- to threefold lower in the former NIL lines as compared to expression in the latter. Together, these data strongly implicate LsNCED4 as the candidate gene responsible for the Htg6.1 phenotype and indicate that decreased ABA biosynthesis at high imbibition temperatures is a major factor responsible for the increased germination thermotolerance of UC96US23 seeds.