wrinkled1: A novel, low-seed-oil mutant of Arabidopsis with a deficiency in the seed-specific regulation of carbohydrate metabolism

Abstract

During oil deposition in developing seeds of Arabidopsis, photosynthate is imported in the form of carbohydrates into the embryo and converted to triacylglycerols. To identify genes essential for this process and to investigate the molecular basis for the developmental regulation of oil accumulation, mutants producing wrinkled, incompletely filled seeds were isolated. A novel mutant locus, wrinkled1 (wri1), which maps to the bottom of chromosome 3 and causes an 80% reduction in seed oil content, was identified. Wild-type and homozygous wri1 mutant plantlets or mature plants were indistinguishable. However, developing homozygous wri1 seeds were impaired in the incorporation of sucrose and glucose into triacylglycerols, but incorporated pyruvate and acetate at an increased rate. Because the activities of several glycolytic enzymes, in particular hexokinase and pyrophosphate-dependent phosphofructokinase, are reduced in developing homozygous wri1 seeds, it is suggested that WRI1 is involved in the developmental regulation of carbohydrate metabolism during seed filling.

Figure 1

Appearance of wild-type (A), wri1–1 (B), and wri1–2 (C) mature seeds.

Figure 2

TLC of lipid extracts from mature seeds of wild type, homozygous mutant wri1–1 and wri1–2 seeds, and F₁ seeds derived from reciprocal crosses between wild-type (Col-2) and mutant plants as indicated. Only the upper portion of the TLC plate is shown. Triacylglycerols (TAG) were visualized by exposure to iodine vapor.

Figure 3

Growth of wild-type (▪), wri1–1 (○), and wri1–2 (▵) mutant plants in soil. For each time point, the fresh weights of aerial parts from six plants were averaged and the ses are indicated.

Figure 4

Time courses of triacylglycerol (TAG), protein, and carbohydrate accumulation in developing seeds of the wild type (▪), wri1–1 (○), and wri1–2 (▵) mutant. A, Triacylglycerols; B, total protein; C, starch; D, Suc; E, Glc; F, Fru. Each time point represents duplicate (A–C) or triplicate (D–F) measurements and ses are indicated.

Figure 5

Incorporation of different precursors into triacylglycerol by developing embryos of the wild type (▪), wri1–1 (○), and wri1–2 mutant (▵). Tested compounds were Suc (A), Glc (B), pyruvate (C), and acetate (D). The rates are expressed as picomoles of precursor converted to triacylglycerol per 20 seeds per hour. Single representative experiments are shown.

Figure 6

Activity of hexokinase (A) and pyrophosphate-dependent phosphofructokinase (PFP) (B) in developing embryos of the wild type (▪) and the wri1–1 (○) mutant. Measurements were done in triplicate and ses are indicated. Prot., Protein.