Poster: Late and Moved Abstracts

Abs # 1360: The overexpression of a novel homeobox gene WHO gives rise to overall malfunction of Arabidopsis meristem maintenance and organ development

Presenter:	Fu, Chiushi , cfu@pop.life.uiuc.edu
Authors	Fu, Chiushi  (A)   Martienssen, Rob  (B)   Bush, Daniel  (A)
Affiliations:	(A): University of Illinois at Urbana-Champaign (B): Cold Spring Harbor Laboratory

We have isolated a novel homeodomain transcription factor gene Wuschel-like Homeodomain Overexpressing (WHO) in Arabidopsis, which shares a high degree of homology to WUSCHEL (WUS), a transcription factor involved in specifying stem cell fate in shoot and floral meristems. WHO encodes a homeodomain protein of 182 amino acids. There are 4 single nucleotide polymorphisms found in Lansberg erecta versus ecotype Columbia, with no amino acid change though. The knock out mutant shows normal growth and development, however an overexpression mutant exhibits a severely stunted phenotype, and defects are observable in shoot, floral and root meristems. The mutant has over-sprouting shoots, malformed leaves, strongly-stunted roots, delayed bolting and flowering, as well as aberrant floral organs. Moreover, callus and somatic embryos form on the petioles and hypocotyls of the mutant plants without any external plant hormone treatment. Morphological studies showed that the mutant root has a radial organization defect, with 7 cortical and endodermal cell files, and nodule-shape lateral roots. Overexpression of WHO upregulates CLAVATA3 (CLV3) and SHOOTMERISTEMLESS (STM) expression, but not WUS and CLAVATA1 (CLV1). Our results indicate that this new homeobox gene is redundant with other homeobox genes, however its misexpression disrupts normal overall development in Arabidopsis, suggesting WHO play an important role in maintaining meristem cell identity and organ formation.