Abstract
The endosperm provides nutrients and growth regulators to the embryo during seed development. LEAFY COTYLEDON1 (LEC1) has long been known to be essential for embryo maturation. LEC1 is expressed in both the embryo and the endosperm; however, the functional relevance of the endosperm-expressed LEC1 for seed development is unclear. Here, we provide genetic and transgenic evidence demonstrating that endosperm-expressed LEC1 is necessary and sufficient for embryo maturation. We show that endosperm-synthesized LEC1 is capable of orchestrating full seed maturation in the absence of embryo-expressed LEC1. Inversely, without LEC1 expression in the endosperm, embryo development arrests even in the presence of functional LEC1 alleles in the embryo. We further reveal that LEC1 expression in the endosperm begins at the zygote stage and the LEC1 protein is then trafficked to the embryo to activate processes of seed maturation. Our findings thus establish a key role for endosperm in regulating embryo development.
Highlights
The endosperm provides nutrients and growth regulators to the embryo during seed development
To investigate if the expression of LEAFY COTYLEDON1 (LEC1) in the endosperm was necessary for seed maturation, we generated seeds with unfertilized endosperms of lec[1] genotype and fertilized diploid embryos of LEC1 genotype using a genomic imprinting bypassing strategy (Fig. 1a), through which small but fully developed seeds could be produced when fis-class mutant flowers were crossed with cdka;[1] mutant pollens[16,17]
The genotypes of the CDKA;1+/+ and cdka;1+/− seeds were confirmed by PCR-based genotyping at the CDKA;1+/cdka;1− and the LEC1+/ lec1− loci in the seedlings derived from each type of seeds (Supplementary Fig. 3e)
Summary
The endosperm provides nutrients and growth regulators to the embryo during seed development. We provide genetic and transgenic evidence demonstrating that endosperm-expressed LEC1 is necessary and sufficient for embryo maturation. We further reveal that LEC1 expression in the endosperm begins at the zygote stage and the LEC1 protein is trafficked to the embryo to activate processes of seed maturation. The endosperm plays an essential role in seed development by nourishing the embryo via transferring maternal nutrients and growth regulators[2]. We hypothesized that the endosperm-expressed LEC1 may act as a molecular signal in the early communication between endosperm and embryo, and subsequently exerts its key roles in activating and regulating various embryo developmental programs. We present the results of our genetic and transgenic experiments designed to test this hypothesis
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