Abstract
HSI2 of Arabidopsis contains B3 DNA-binding domain and the C-terminal EAR motif that mediate active transcriptional repression. Although disruptant of a gene for HSI2 and that of a gene for its closely related HSL1 both grow normally, seeds of double knockouts of hsi2 and hsl1 (KK mutant) obtained by a genetic cross stop growth 7 days after germination. The KK mutant express LEC class of master regulators and seed maturation-specific genes 4 days after germination in a sugar-dependent manner, and accumulate seed storage proteins and oil in swollen hypocotyls. It is suggested that HSI2 and HSL1 share important functions to repress the seed maturation program after germination. Expression of HSI2p:GUS and HSL1p:GUS showed overlapping patterns in various tissues including embryos. We introduced dexamethasone (DEX)-inducible RNAi for HSL1 in hsi2 mutant. This transformant, germination of seeds in the presence of DEX caused swelling of hypocotyls and severe growth retardation.
