Rice bicoid-related cDNA sequence and its expression during early embryogenesis

Abstract

Bicoid is one of the important Drosophila maternal genes involved in the control of embryo polarity and larvae segmentation. To clone and characterize the rice bicoid-related genes, one cDNA clone, Rb24 (EMBL accession number: AJ2771380), was isolated by screening of rice unmature seed cDNA library. Sequence analysis indicates that Rb24 contains a putative amino acid sequence, which is homologous to unique 8 amino acids sequence within Drosophila bicoid homeodomain (50% identity, 75% similarity) and involves a lys-9 in putative helix 3. Northern blot analysis of rice RNA has shown that this sequence is expressed in a tissue-specific manner. The transcript was detected strongly in young panicles, but less in young leaves and roots. This results are further confirmed with paraffin section in situ hybridization. The signal is intensive in rice globular embryo and located at the apical tip of the embryo, then, along with the development of embryo, the signal is getting reduced and transfers into both sides of embryo. The existence of bicoidrelated sequence in rice embryo and the similarity of polar distribution of bicoid and Rb24 mRNA in early embryo development may implicates a conserved maternal regulation mechanism of body axis presents in Drosophila and in rice.

Transcription factors regulating the progression of monocot and dicot seed development

“…In the early rice embryo, polarity formation and establishment of the apical-basal axis is controlled by RICE BICOID 24/RB24. It expresses mainly in the early globular embryo and later shows a dorso-ventral pattern [46]. Radial axis differentiation is indicated by HAZ1, which is expressed most in the outer layers of the globular embryo at 3 DAP and becomes more intense in the ventral parts at 4 and 5 DAP, thus marking the outer layer of cells before the commencement of morphological differentiation [47].…”