WAG, a wheat AGAMOUS homolog, is associated with development of pistil-like stamens in alloplasmic wheats

Abstract

Pistillody, homeotic transformation of stamens into pistil-like structures, has been reported in cytoplasmic substitution (alloplasmic) lines of common wheat (Triticum aestivum) with Aegilops crassa cytoplasm. The induction of pistillody is suppressed by the Rfd1 gene detected on the long arm of chromosome 7B in wheat cultivar 'Chinese Spring' (CS). Because of the absence of Rfd1, the alloplasmic line CS ditelosomic 7BS [(cr)-CSdt7BS] lacking the long arm of chromosome 7B exhibits pistillody in all florets, whereas the euplasmic CS ditelosomic 7BS (CSdt7BS) with normal cytoplasm forms normal stamens. To study the molecular mechanism of pistillody caused by nuclear-cytoplasm interaction in alloplasmic wheat, we cloned and characterized a wheat AGAMOUS homolog, WAG. The WAG gene copy number in the wheat genome was estimated at three, located on the homoeologous group 1 chromosomes. Northern blot analysis with a normal wheat line revealed that the transcription level of WAG was lower in young spikes and increased during spike development. The highest expression was observed in spikes at the booting to heading stage. The 1.1 kb WAG transcript accumulated in both the reproductive (pistil and stamen) and non-reproductive (palea and lemma) portions of spikes at the heading stage, whereas an extra transcript of different molecular size (1.3 kb) was observed in pistil-like stamens of line (cr)-CSdt7BS as well as in pistils of CSdt7BS and (cr)-CSdt7BS. These results suggest that the product of the 1.3 kb WAG transcript is involved in pistil development and is associated with pistillody caused by a nuclear-cytoplasm interaction in alloplasmic wheat.