Asymmetric cues in plants
The plant life cycle alternates between the diploid, spore-producing stage (sporophyte) and the haploid, gamete-producing stage (gametophyte). In contrast to other land plants, flowering plants (angiosperms) produce highly reduced gametophytes, with gametes capable of double fertilization. During double fertilization, angiosperms form seeds with a single diploid embryo and endosperm, a tissue with highly variable ploidy. Although gametophyte development is a fundamental process in the plant life cycle, the underlying molecular mechanisms are not well understood. Now, Pagnussat et al. (Science published online, doi: 10.1126/science.1167324; 4 June 2009) report that asymmetric distribution of the phytohormone auxin is critical for establishing cell fate within the female gametophyte (embryo sac) in Arabidopsis. The authors followed expression of auxin using a GFP reporter under the control of DR5, an auxin responsive promoter, and saw polarized accumulation of GFP at the micropylar pole of the embryo sac. Perturbing the asymmetric distribution of auxin by ectopically expressing key enzymes in auxin biosynthesis led to abnormal patterning within embryo sacs. In addition, disrupting genes that mediate the auxin response induced switching between cell fates. The study suggests that cell fate specification in the Arabidopsis embryo sac may be regulated by a morphogenetic mechanism that relies on positional cues conferred by distance from the auxin source. PC
This is a preview of subscription content, access via your institution
