Genetics of seed quality

Till present plant breeders hardly incorporate seed quality as an important trait in their breeding programs. The selection is at most indirect, since non-germinating seeds are by nature eliminated in the selection process.

With the increased know how on molecular aspects of seed germination, sequencing of an increasing number of plant genomes, further developments in marker assisted breeding and increasing tools for quantitative genetics, it should become more and more feasible to incorporate also seed quality in breeding programs.

We tested this hypothesis using Arabidopsis thaliana as a model system. With this model plant a large amount of genetic variation is present for different aspects regarding seed quality. This is available in the form of many mutants (including T-TNA tagged mutants) and ecotypes.

Since Arabidopsis is not a crop, we first needed to develop a seed quality assay (Tesnier et al., 2002. Seed Science and Technology 30: 149-165). Also a controlled deterioration test was developed to analyse genetic variation in seed storability.

The ecotypes Landsberg erecta (Le) and Cape Verdian Island differ with respect to seed dormancy. In testing different ecotypes for seed storability, we oserved that Cvi seeds exhibited a longer storability compared to Le seeds. In a separate study it was demonstrated that the levels of the oligosaccharides raffinose and stachiose are lower in Cvi seeds. These oligosaccharides have been hypothesized to be important for seed desiccation tolerance. To study the genetic relation between seed dormancy, storability and oligosaccharide content, we performed a QTL analysis using Recombinant Inbred Lines descending from a cross between these two parents. The results of these analyses showed that both ecotypes had loci on their genome that significantly contributed to seed dormancy and storability, both in positive and negative ways. Most of the loci effecting storability or dormancy were not linked. There was no effect of the locus influencing oligosaccharide levels on either storability or dormancy (Bentsink et al., 2000. Plant Physiology 124: 1595-1604).

Storability is also studied with mutants (Clerkx, 2004). Mutants with a reduced level of anti-oxidants, such as vitamin-C, glutathion, catalase and flavonoids, which were claimed to be important for seed storability, had very little effect on this trait (Clerkx et al 2004a). A new green-seeded mutant showed that the quality of seeds with reduced breakdown of chlorophyll is reduced (Clerkx et al 2003). By selecting better storable variants of mutant seeds with a very short storability, it was possible to identify genes affecting seed storability (Clerkx, 2004). The use of natural variation and quantitative trait locus (QTL) analysis identified additional loci for seed quality (Clerkx et al 2004b). The genetic identification of genes involved in seed quality using the different approaches described in these studies may lead to the molecular cloning of these genes in the future.

Related recent publications

• Clerkx, E.J.M., H. Blankestijn-de Vries, G.J. Ruys, S.P.C. Groot & M. Koornneef. 2004. Genetic differences in seed longevity of various Arabidopsis mutants. Phys. Plantarum 121: 448-461.   
  
• Clerkx, E.J., M.E. El-Lithy, E. Vierling, G.J. Ruys, H. Blankestijn-De Vries, S.P.C. Groot, D. Vreugdenhil & M. Koornneef. 2004. Analysis of natural allelic variation of Arabidopsis seed germination and seed longevity traits between the accessions Landsberg erecta and Shakdara, using a new recombinant inbred line population. Plant Physiol.135(1):432-43.
• Clerkx E.J.M.. 2004. The genetics of seed quality in Arabidopsis thaliana. PhD thesis Wageningen University.
• Clerkx EJM, Vries HB, Ruys GJ, Groot SPC, Koornneef M.  2003. Characterization of green seed, an enhancer of abi3-1 in Arabidopsis that affects seed longevity. Plant Physiol. 132: 1077-1084.