Expression differences between normal and indeterminate1 maize suggest downstream targets of ID1, a floral transition regulator in maize.

The INDETERMINATE1 (ID1) transcription factor is a key regulator of the transition to flowering in maize. ID1 is expressed in immature leaves where it controls the production or transmission of leaf-derived florigenic signals. Loss-of-function id1 mutants make many more leaves than normal plants and produce aberrant flowers; however, they exhibit no obvious developmental defects in early growth stages. A maize oligonucleotide microarray was used to assess the molecular differences between immature leaves of wild-type and id1 mutant plants prior to the floral transition. This analysis revealed 55 genes with a significant 2-fold difference in expression; 22 are down-regulated and 33 are up-regulated in id1 mutants. Most prominent is a novel family of three beta-glucosidase genes that are most closely related to sorghum dhurrinases. These genes, termed Zmdhr1, Zmdhr2, and Zmdhr3, are undetectable in immature leaves of id1 mutants and are expressed exclusively in normal immature leaves in a pattern identical to the ID1 gene. Other down-regulated genes include a group of four zinc finger protein-encoding genes that are unrelated to ID1. A significant number of genes up-regulated in id1 mutant immature leaves have potential roles in photosynthesis and carbon fixation, substantiating a possible connection between floral induction and assimilate partitioning. Finally, expression of these genes was compared in florally induced versus uninduced teosinte, a photoperiod-sensitive progenitor of day-neutral maize. Only a few genes showed expression differences, suggesting that ID1 acts in a novel autonomous floral induction pathway that is distinct from the photoperiod induction pathway.