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Seed dormancy allows seeds to overcome periods that are unfavourable for seedling established and is therefore important for plant ecology and agriculture. Several processes are known to be involved in the induction of dormancy and in the switch from the dormant to the germinating state. The role of plant hormones, the different tissues and genes involved, including newly identified genes in dormancy and germination are described in this chapter, as well as the use transcriptome, proteome and metabolome analyses to study these mechanistically not well understood processes.

The seed is the structure in which a usually fully developed plant embryo is dispersed and that enables it to survive the period between seed maturation and establishment of the next generation as a seedling after it has germinated. The dry, quiescent seed is well equipped to sustain extended periods of unfavorable conditions. Dormancy, defined as the failure of an intact viable seed to complete germination under conditions favorable for germination, is an adaptive trait optimizing germination to the best suitable time that enables the species to complete its life cycle. The environmental conditions required for germination are not defined specifically, but in practice refer to conditions that allow germination of a nondormant seed batch of the species under investigation.

The study of the intraspecific natural variation existing in Arabidopsis provides a useful resource for the dissection of its genome at the functional, ecological, and evolutionary levels. A major step in these studies is the identification and location of quantitative trait loci (QTLs) determining the variation for trait(s) of interest, so-called QTL analysis. Here we provide general methods to achieve this goal, including (1) the selection of wild accessions that can serve as parental lines for QTL mapping; (2) the development of mapping populations; (3) the construction of the required genomewide linkage maps of the populations; and (4) the mapping and characterization of QTLs affecting the trait(s).

The definition of gene functions requires the phenotypic characterization of genetic variants. Currently, such functional analysis of Arabidopsis genes is based largely on laboratory-induced mutants that are selected in forward and reverse genetic studies. An alternative complementary source of genetic variation is available: the naturally occurring variation among accessions. The multigenic nature of most of this variation has limited its application until now. However, the use of genetic methods developed to map quantitative trait loci, in combination with the characteristics and resources available for molecular biology in Arabidopsis, allow this variation to be exploited up to the molecular level. Here, we describe the current tools available for the forward genetic analysis of this variation, and review the recent progress in the detection and mapping of loci and the cloning of large-effect genes

*INRA Laboratoire de Biologie des Semences Versailles Diffusion du document : INRA Laboratoire de Biologie des Semences Versailles

Abscisic acid (ABA) is a plant hormone involved in seed development and germination and in responses to various environmental stresses. The last step of ABA biosynthesis involves oxidation of abscisic aldehyde, and aldehyde oxidase (EC 1.2.3.1) is thought to catalyze this reaction. An aldehyde oxidase isoform, AO, encoded by AAO3, one of four Arabidopsis aldehyde oxidase genes (AAO1, AAO2, AAO3, and AAO4), is the most likely candidate for the enzyme, because it can efficiently catalyze the oxidation of abscisic aldehyde to ABA. Here, we report the isolation and characterization of an ABA-deficient Arabidopsis mutant that maps at the AAO3 locus. The mutant exhibits a wilty phenotype in rosette leaves, but seed dormancy is not affected. ABA levels were significantly reduced in the mutant leaves, explaining the wilty phenotype in rosettes, whereas the level in the mutant seeds was less reduced. No AO activity could be detected in the rosette leaves of the mutant. Sequence data showed that the mutant contains a G to A substitution in the AAO3 gene. The mutation causes incorrect splicing of the ninth intron of AAO3 mRNA. We thus conclude that the ABA-deficient mutant is impaired in the AAO3 gene and that the gene product, AO, is an aldehyde oxidase that catalyzes the last step of ABA biosynthesis in Arabidopsis, specifically in rosette leaves. Other aldehyde oxidases may be involved in ABA biosynthesis in other organs.

This invention relates to the determination, cloning and expression of the flowering time gene FWA and the use of this gene to delay or accelerate flowering in a large variety of plant species. Specifically the gene that was determined is that of Arabidopsis thaliana. Naturally the invention extends to other plants as well.