Functional conservation of wheat orthologs of maize rough sheath1 and rough sheath2 genes.

Maize rough sheath2 (RS2) and Arabidopsis ASYMMETRIC LEAVES1 (AS1) both encode a Myb transcription factor and repress Knotted1-type homeobox (KNOX) genes. The RS2/AS1-KNOX relationship is functionally conserved between maize and Arabidopsis. Here, we cloned wheat orthologs of RS2/AS1 and of a maize rough sheath1 (rs1) KNOX gene and named them WRS2 and WRS1, respectively. WRS1 mRNA was detected at leaf insertion points of the vegetative shoot meristem but was missing in differentiating floral organs. Conversely, WRS2 transcripts accumulated in initiating and developing floral organs. Transgenic tobacco plants expressing WRS1 showed morphological alterations typically observed due to expression of other KNOX genes. WRS2 with a deletion of the Myb domain could interact with NtPHAN to form a heterodimer, and expression of the truncated WRS2 gene conferred a dominant-negative phenotype similar to that expected and induced ectopic expression of an endogenous KNOX gene. Moreover, WRS2 expression alleviated morphological alterations in tobacco plants expressing the wheat KNOX gene. Therefore, the WRS2 gene product represses KNOX expression. These results indicate that the WRS2-KNOX relationship plays a fundamentally important role in lateral organ initiation and differentiation of meristems in wheat development. The antagonistic relationship between WRS2 and KNOX around meristematic tissues has been functionally conserved during wheat evolution.