Genetic analysis of seed-soluble oligosaccharides in relation to seed storability of Arabidopsis

Abstract

Seed oligosaccharides (OSs) and especially raffinose series OSs (RSOs) are hypothesized to play an important role in the acquisition of desiccation tolerance and consequently in seed storability. In the present work we analyzed the seed-soluble OS (sucrose, raffinose, and stachyose) content of several Arabidopsis accessions and thus identified the genotype Cape Verde Islands having a very low RSO content. By performing quantitative trait loci (QTL) mapping in a recombinant inbred line population, we found one major QTL responsible for the practically monogenic segregation of seed stachyose content. This locus also affected the content of the two other OSs, sucrose, and raffinose. Two candidate genes encoding respectively for galactinol synthase and raffinose synthase were located within the genomic region around this major QTL. In addition, three smaller-effect QTL were identified, each one specifically affecting the content of an individual OS. Seed storability was analyzed in the same recombinant inbred line population by measuring viability (germination) under two different seed aging assays: after natural aging during 4 years of dry storage at room temperature and after artificial aging induced by a controlled deterioration test. Thus, four QTL responsible for the variation of this trait were mapped. Comparison of the QTL genetic positions showed that the genomic region containing the major OS locus did not significantly affect the seed storability. We concluded that in the studied material neither RSOs nor sucrose content had a specific effect on seed storability.

Figure 1

Seed-soluble OS content of 10 Arabidopsis accessions, Wassilewksija-1 (Ws-1), Columbia-1 (Col-1), Catania-1 (Ct-1), C24, Eilenburg-0 (Eil-0), Ler, Martuba-1 (Mt-1), Shahdara (Shah), Rschew-1 (RLD-1), and Cape Verde Islands (Cvi). Columns correspond to means of two measurements of bulked seeds from six plants; vertical bars indicate the range of variation.

Figure 2

Frequency distributions of Suc, raffinose, and stachyose content in seeds of the Ler/Cvi RIL population. Arrows correspond to the parental line means and horizontal bars represent their ranges of variation.

Figure 3

Soluble OS content in hybrid seeds obtained from reciprocal crosses between Ler and Cvi (means of two measurements; vertical bars indicate the range of variation).

Figure 4

QTL likelihood maps for seed-soluble OS contents of the five linkage groups of Arabidopsis. The abscissas correspond to the genetic maps in cM; 1 through 5 indicate the linkage group number. The horizontal dotted lines correspond to the LOD score threshold of 2.8 used to declare the presence of a QTL. Two-LOD support intervals for the significant QTL are shown as black bars along the abscissas. QTL effects are shown for linkage groups 1 and 3 where the major QTL are located. These are given as twice the additive allele effects, i.e. as the mean differences between the two RIL genotypic groups carrying the Ler and Cvi alleles. A positive QTL effect represents that the Ler allele increases the content. The percentage of phenotypic variance explained by each QTL is reported close to the corresponding LOD score peak.

Figure 5

Frequency distribution of the seed viability (germination percentage) of the Ler/Cvi RIL after the CDT. Arrows correspond to the parental line means, and horizontal bars represent their ranges of variation.

Figure 6

QTL likelihood maps for seed storability measured as viability after the CDT (solid line) and 4 years of natural aging (dashed line). The abscissas correspond to the genetic maps in cM (the linkage group number being indicated in the right upper corner of each panel). Horizontal dotted lines correspond to the LOD score threshold of 2.8 used to declare the presence of a QTL. Two-LOD support intervals for the significant QTLs are shown as black bars along abscissas. The additive QTL effects are expressed as probit units of the germination percentage after the CDT. These are estimated as the mean differences between the two RIL genotypic groups carrying the Ler and Cvi alleles (a positive value implies Ler increases the corresponding phenotypic value). The percentage of variance explained by each QTL is reported close to the corresponding LOD score peak.

Figure 7

Ler/Cvi linkage map showing the genetic location of QTL affecting seed-soluble OS contents and seed storability. Arrows indicate the direction of Ler allele phenotypic effect (up, increasing; down, decreasing). The length of the arrows depicts the 2-LOD support intervals. The horizontal black arrow points to the major OS QTL.