Characterization of wheat Bell1-type homeobox genes in floral organs of alloplasmic lines with Aegilops crassa cytoplasm

In this study, four wheat Bell1-like homeobox (BLH) genes were isolated and named WBLH1 to WBLH4. WBLH1/WBLH3/WBLH4 expression was observed in the basal boundary region of the ovary in both normal pistils and transformed stamens. WBLH2 was also strongly expressed in integuments not only of normal ovules in pistils but also of the ectopic ovules in transformed stamens, and the WBLH2 expression pattern in the sterile pistils seemed to be identical to that in normal ovules of fertile pistils. In addition, WBLH1 and WBLH3 showed interactions with the three wheat KNOX proteins through the BEL domain. WBLH2, however, formed a complex with wheat KNOTTED1 and ROUGH SHEATH1 orthologs through SKY and BEL domains, but not with a wheat LIGULELESS4 ortholog.Expression of the four WBLH genes is evident in reproductive organs including pistils and transformed stamens and is independent from female sterility in alloplasmic wheat lines with Ae. crassa cytoplasm. KNOX-BLH interaction was conserved among various plant species, indicating the significance of KNOX-BLH complex formation in wheat developmental processes. The functional features of WBLH2 are likely to be distinct from other BLH gene functions in wheat development.Alien cytoplasm largely alters gene expression profiles, affecting growth and organogenesis. Nuclear-cytoplasm incompatibility results in abnormal growth phenotypes in higher plants [1,2]. Recurrent backcrossing has been commonly used for production of nuclear-cytoplasmic substitution plants called alloplasmic lines, in which the cytoplasmic genomes are replaced by ones from a related species [3]. Cytoplasmic male sterility is a major phenomenon among the abnormal phenotypes of the alloplasmic lines [1,4]. In many cases of cytoplasmic male sterility, nuclear-cytoplasm incompatibility induces abortion of pollen. Homeotic transformation of stamens into pistil-like structures is sometimes observed in alloplasmic lines of carrot, Brassica napus, tobacco and wheat [5-9