Mutation of the transcription factor LEAFY COTYLEDON 2 alters the chemical composition of Arabidopsis seeds, decreasing oil and protein content, while maintaining high levels of starch and sucrose in mature seeds

Abstract

The transcription factor LEAFY COTYLEDON 2 (LEC2; At1g28300) is preferentially expressed in developing seeds of Arabidopsis. Detailed biochemical analysis of a loss-of-function lec2 mutant was carried out in seeds 6-21 days after flowering (DAF). In comparison to wild type controls, lec2 seeds had 15% less protein and 30% less oil, but accumulated 140% more sucrose and >5-fold more starch. We also quantified biomass and carbohydrates in the seed coat and embryo. The lec2 mutant had smaller seeds and an altered proportion of dry weight (bigger seed coat and smaller embryos). Mutant plants produced less mature seeds per silique and the harvest index was reduced. Soluble sugars (glucose, fructose and sucrose) was accumulated in the seed coat of the lec2 mutant, whereas the opposite effect was observed in the embryos (decrease in comparison to wild type). The rate of starch synthesis increased during early development, whereas the rate of starch degradation was diminished during late development, leading to higher residual starch in mature seed of the mutant. Starch accumulated in both seed coat and embryo. Homozygous mutant plants produced seeds that could germinate well if they were harvested immaturely, whereas seeds that became dry during maturity lost their germination efficiency very rapidly. We conclude that the LEC2 transcription factor not only controls cotyledon identity and morphology as previously reported, but also alters: (1) the delivery of photosynthates from the seed coat to the embryo (sink strength), (2) carbon partitioning towards different storage compounds (oil, proteins and carbohydrates), (3) the rate of starch synthesis and degradation in developing seeds and (4) germination capacity of dry seeds.