LACHESIS restricts gametic cell fate in the female gametophyte of Arabidopsis.

In flowering plants, the egg and sperm cells form within haploid gametophytes. The female gametophyte of Arabidopsis consists of two gametic cells, the egg cell and the central cell, which are flanked by five accessory cells. Both gametic and accessory cells are vital for fertilization; however, the mechanisms that underlie the formation of accessory versus gametic cell fate are unknown.

An egg apparatus-specific enhancer of Arabidopsis, identified by enhancer detection.

Despite a central role in angiosperm reproduction, few gametophyte-specific genes and promoters have been isolated, particularly for the inaccessible female gametophyte (embryo sac). Using the Ds-based enhancer-detector line ET253, we have cloned an egg apparatus-specific enhancer (EASE) from Arabidopsis (Arabidopsis thaliana). The genomic region flanking the Ds insertion site was further analyzed by examining its capability to control gusA and GFP reporter gene expression in the embryo sac in a transgenic context.

Analysis of transposon insertion mutants highlights the diversity of mechanisms underlying male progamic development in Arabidopsis.

To identify genes with essential roles in male gametophytic development, including postpollination (progamic) events, we have undertaken a genetic screen based on segregation ratio distortion of a transposon-borne kanamycin-resistance marker. In a population of 3359 Arabidopsis Ds transposon insertion lines, we identified 20 mutants with stably reduced segregation ratios arising from reduced gametophytic transmission. All 20 mutants showed strict cosegregation of Ds and the reduced gametophytic transmission phenotype.

Maternal control of embryogenesis by MEDEA, a polycomb group gene in Arabidopsis.

The gametophytic maternal effect mutant medea (mea) shows aberrant growth regulation during embryogenesis in Arabidopsis thaliana. Embryos derived from mea eggs grow excessively and die during seed desiccation. Embryo lethality is independent of the paternal contribution and gene dosage.