Abstract
In Oryza sativa (rice), floral organs such as stamens and carpels are enclosed by the lemma and palea. On the top of the lemma, a needle-like structure, called awn, is formed in O. sativa L. ssp. indica and wild rice species. The awn sharpens at the tip and connects to the midrib of the lemma at the base. Molecular mechanisms underlying awn development are not known. To understand the mechanisms regulating development of the awn, we focused on two genes, DROOPING LEAF (DL) and SHOOTLESS2 (SHL2). The DL gene, a member of the YABBY gene family, encodes a plant specific transcriptional factor and is known to have a crucial function in midrib formation and carpel specification. The SHL2 gene encodes an enzyme responsible for trans-acting siRNA synthesis.
Our genetic analyses revealed that DL had a role to promote awn formation, in addition to the well-known functions of DL. Although DL was specifically expressed in the midrib in the lemma, as it is in the leaves, its expression was not detected in the developing awn itself, suggesting that DL acts to form the awn through a non-cell autonomous mechanism. By contrast, the SHL2 gene negatively regulated awn formation.
