Genetic variation for lettuce seed thermoinhibition is associated with temperature-sensitive expression of abscisic Acid, gibberellin, and ethylene biosynthesis, metabolism, and response genes.

Jason Argyris,Eiji Hayashi,Kent J Bradford,David W Still,Peetambar Dahal

doi:10.1104/pp.108.125807

Jason Argyris, Eiji Hayashi + Show 3 more

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https://doi.org/10.1104/pp.108.125807

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Abstract

Lettuce (Lactuca sativa 'Salinas') seeds fail to germinate when imbibed at temperatures above 25 degrees C to 30 degrees C (termed thermoinhibition). However, seeds of an accession of Lactuca serriola (UC96US23) do not exhibit thermoinhibition up to 37 degrees C in the light. Comparative genetics, physiology, and gene expression were analyzed in these genotypes to determine the mechanisms governing the regulation of seed germination by temperature. Germination of the two genotypes was differentially sensitive to abscisic acid (ABA) and gibberellin (GA) at elevated temperatures. Quantitative trait loci associated with these phenotypes colocated with a major quantitative trait locus (Htg6.1) from UC96US23 conferring germination thermotolerance. ABA contents were elevated in Salinas seeds that exhibited thermoinhibition, consistent with the ability of fluridone (an ABA biosynthesis inhibitor) to improve germination at high temperatures. Expression of many genes involved in ABA, GA, and ethylene biosynthesis, metabolism, and response was differentially affected by high temperature and light in the two genotypes. In general, ABA-related genes were more highly expressed when germination was inhibited, and GA- and ethylene-related genes were more highly expressed when germination was permitted. In particular, LsNCED4, a gene encoding an enzyme in the ABA biosynthetic pathway, was up-regulated by high temperature only in Salinas seeds and also colocated with Htg6.1. The temperature sensitivity of expression of LsNCED4 may determine the upper temperature limit for lettuce seed germination and may indirectly influence other regulatory pathways via interconnected effects of increased ABA biosynthesis.

Highlights

Lettuce (Lactuca sativa ‘Salinas’) seeds fail to germinate when imbibed at temperatures above 25°C to 30°C
Only UC96US23 seeds germinated at 35°C in the light, germination was delayed and less uniform at this temperature compared with 20°C, beginning after
The Pfr requirement for germination increases as the temperature increases (Fielding et al, 1992; Kristie and Fielding, 1994) and the seeds become more sensitive to inhibition by abscisic acid (ABA) (Roth-Bejerano et al, 1999; Gonai et al, 2004)

Summary

Introduction

Lettuce (Lactuca sativa ‘Salinas’) seeds fail to germinate when imbibed at temperatures above 25°C to 30°C (termed thermoinhibition). Comparative genetics, physiology, and gene expression were analyzed in these genotypes to determine the mechanisms governing the regulation of seed germination by temperature. The temperature sensitivity of expression of LsNCED4 may determine the upper temperature limit for lettuce seed germination and may indirectly influence other regulatory pathways via interconnected effects of increased ABA biosynthesis. Lettuce (Lactuca sativa) seeds exhibit thermoinhibition (fail to germinate) at temperatures well below the biological upper limit for seedling growth (Cantliffe et al, 1981). GA, and red light can increase the upper temperature limit of lettuce seed germination, and exposure to ABA can decrease it (Reynolds and Thompson, 1973; Saini et al, 1986, 1989; Dutta and Bradford, 1994; Kristie and Fielding, 1994; Gonai et al, 2004). The sensitivity of lettuce seed germination to inhibition by ABA is enhanced at higher temperatures (Robertson and Berrie, 1977; Roth-Bejerano et al, 1999)

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