A genetic locus and gene expression patterns associated with the priming effect on lettuce seed germination at elevated temperatures

Abstract

Seeds of most cultivated varieties of lettuce (Lactuca sativa L.) fail to germinate at warm temperatures (i.e., above 25–30°C). Seed priming (controlled hydration followed by drying) alleviates this thermoinhibition by increasing the maximum germination temperature. We conducted a quantitative trait locus (QTL) analysis of seed germination responses to priming using a recombinant inbred line (RIL) population derived from a cross between L. sativa cv. Salinas and L. serriola accession UC96US23. Priming significantly increased the maximum germination temperature of the RIL population, and a single major QTL was responsible for 47% of the phenotypic variation due to priming. This QTL collocated with Htg6.1, a major QTL from UC96US23 associated with high temperature germination capacity. Seeds of three near-isogenic lines (NILs) carrying an Htg6.1 introgression from UC96US23 in a Salinas genetic background exhibited synergistic increases in maximum germination temperature in response to priming. LsNCED4, a gene encoding a key enzyme (9-cis-epoxycarotinoid dioxygenase) in the abscisic acid biosynthetic pathway, maps precisely with Htg6.1. Expression of LsNCED4 after imbibition for 24 h at high temperature was greater in non-primed seeds of Salinas, of a second cultivar (Titan) and of NILs containing Htg6.1 compared to primed seeds of the same genotypes. In contrast, expression of genes encoding regulated enzymes in the gibberellin and ethylene biosynthetic pathways (LsGA3ox1 and LsACS1, respectively) was enhanced by priming and suppressed by imbibition at elevated temperatures. Developmental and temperature regulation of hormonal biosynthetic pathways is associated with seed priming effects on germination temperature sensitivity.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-009-9591-x) contains supplementary material, which is available to authorized users.

Aspectos fisiológicos e bioquímicos da germinação de sementes de alface em diferentes temperaturas

“…A cultivar Hortência foi a que apresentou menor atividade dessa enzima. Schwember & Bradford (2010) observaram que a cultivar Dark Green Boston, considerada termossensível, também apresentou menor atividade da endo-β-mananase. De acordo com Nascimento et al (2004), essa enzima é responsável pelo enfraquecimento das paredes celulares do endosperma das sementes de alface quando germinadas a temperaturas elevadas; com isso, genótipos termotolerantes apresentam maior atividade enzimática do que aqueles termossensíveis.…”

Genetic Variation for Thermotolerance in Lettuce Seed Germination Is Associated with Temperature-Sensitive Regulation of ETHYLENE RESPONSE FACTOR1 (ERF1)

“…In many crops, domestication has largely eliminated these natural dormancy mechanisms, but in others, such as lettuce, they persist and can cause problems for germination and synchronous crop establishment when temperatures exceed permissive limits . Physiological treatments such as seed priming (prehydration and drying) can overcome such temperature-induced inhibition of germination (Schwember and Bradford, 2010), but a more general approach would be to identify the genetic and physiological mechanisms underlying such thermoinhibition and develop cultivars that no longer exhibit the trait. In previous work, we identified a QTL (Htg6.1) and its underlying gene (LsNCED4) from the progenitor species of lettuce (L. serriola) that demonstrated the critical role of ABA in preventing germination at high temperatures (Argyris et al, 2005(Argyris et al, , 2008(Argyris et al, , 2011Huo et al, 2013) and identified natural alleles that can be used by breeders to ameliorate seed thermoinhibition in lettuce Figure 6.…”

“…The thermotolerance phenotype of Lactuca serriola US96UC23 (formerly reported as UC96US23), an accession of the wild progenitor species of lettuce, has been dissected genetically (Argyris et al, 2005;Truco et al, 2007), leading to the identification of a gene encoding an enzyme involved in the biosynthesis of abscisic acid (ABA), 9-CIS-EPOXYCAROTENOID DIOXYGENASE4 (LsNCED4), as the causal gene (Argyris et al, 2008(Argyris et al, , 2011Huo et al, 2013). While lettuce seed thermoinhibition can be alleviated by seed prehydration (priming) under low temperatures (Schwember and Bradford, 2010), eliminating seed thermoinhibition in lettuce cultivars by incorporating natural genetic variation would be an effective approach to improve crop establishment and lettuce production and ameliorate the effects of rising global temperatures.…”

Thermoinhibition in parsley seeds

“…According to Kozarewa et al (2006), when lettuce seeds are exposed to high temperatures during imbibition, there may be temporary (thermoinhibition) or complete germination inhibition, in which seeds do not germinate even after lowering temperature (thermodormancy). Several studies have reported the causes of this sensitivity and the existence of a close link between endosperm weakening, activity of endo-β-mannanase enzyme, ethylene production, heattolerant proteins such as heat shock proteins (HSP) and germination of lettuce seeds under high temperatures (NASCIMENTO;CANTLIFFE, 2002;NASCIMENTO et al, 2004;SCHWEMBER;BRADFORD, 2010;CATÃO et al, 2014). Other authors have focused their studies on sensitivity to high temperatures of germinating seeds with hormonal balance.…”