whitehead home > research news > search news archives > 2006 news stories > when rna rules > microrna expression in arabidopsis thaliana seedlings   A class of tiny molecules called microRNAs plays a major role in plant development, as seen in these Arabidopsis thaliana seedlings grown by Whitehead postdoctoral fellow Allison Mallory. She achieved dramatic results by overexpressing a single microRNA gene. The mutant plants (left and right) have fused seed leaves that form cup-shaped structures.