HUA1, a regulator of stamen and carpel identities in Arabidopsis, codes for a nuclear RNA binding protein.

Stamen and carpel identities are specified by the combinatorial activities of several floral homeotic genes, APETALA3, PISTILLATA, AGAMOUS (AG), SEPALLATA1 (SEP1), SEPALLATA2 (SEP2), and SEPALLATA3 (SEP3), all of which code for MADS domain DNA binding proteins. AG and the SEP genes also control floral determinacy. HUA1 and HUA2 were identified previously as regulators of stamen and carpel identities and floral determinacy because the recessive hua1-1 or hua2-1 allele affected these processes in plants with a lower dosage of functional AG (either homozygous for the weak ag-4 allele or heterozygous for the strong ag-1 allele). HUA2 was cloned previously and shown to code for a novel protein. We isolated the HUA1 gene using a map-based approach and show that it encodes a protein with six CCCH-type zinc finger motifs that is also found in yeast, Caenorhabditis elegans, Drosophila melanogaster, and mammalian proteins. Several such genes from invertebrates and mammals are known to play key regulatory roles in development. Therefore, HUA1 are another example of non-MADS domain proteins involved in organ identity specification. We demonstrated that HUA1 binds ribohomopolymers, preferentially poly rU and poly rG, but not double-stranded DNA in vitro. This finding suggests that HUA1, like several mammalian CCCH zinc finger proteins, is an RNA binding protein. Therefore, HUA1 likely participates in a new regulatory mechanism governing flower development.