Changes in gene expression in the leafy cotyledon1 (lec1) and fusca3 (fus3) mutants of Arabidopsis thaliana L.

Arabidopsis thaliana L. leafy cotyledon1 (lec1) and fusca3 (fus3) mutants s how multiple phenotypic defects during seed development. In this report the effects of these mutations are examined at the molecular level. The patter ns of protein accumulation in led and fus3 seeds are severly altered. In le d seeds the steady-state mRNA levels of several late embryogenesis genes we re reduced. Different patterns of expression were observed, indicating the occurrence of several regulatory pathways. The effect of led mutations on t he expression of the late-embryogenesis abundant AtEm1 gene was examined in detail. In lec1-1 seeds, the AtEm1 gene was expressed at a higher level th an in the wild type and earlier in development. The activity of an AtEm1 pr omoter/beta-glucuronidase reporter gene construct in transgenic A. thaliana plants was studied. Changes in promoter activity in lec1-1 with respect to wild-type seeds were correlated with changes in corresponding mRNA steady- state levels. fus3-2 mutation produced similar changes in AtEm1 promoter ac tivity as lec1-1, which is consistent with the hypothesis that LEC1 and FUS 3 might act in the same regulatory pathway. Transgenic analysis using 5'-pr omoter deletions demonstrated that at least two regions of AtEm1 gene promo ter interact with the LEC1-dependent transcriptional regulatory pathway. In spite of expression of the AtEm1 promoter and accumulation of AtEm1 mRNA, the corresponding Em1 protein does not accumulate in lec1-1 seeds. The ADA inducibility of the AtEm1 promoter was not affected by the led mutation.