Molecular cloning and expression analysis of the replacement histone H3 gene of Italian ryegrass (Lolium multiflorum).

The replacement histone H3 gene and its 5'-flanking sequence were isolated from Italian ryegrass by polymerase chain reaction and inverse polymerase chain reaction, respectively. Expression analysis showed that this gene is constitutively expressed in the entire plant. The expression level in leaves was found to be significantly low when compared with that in other tissues. However, the gene expression level in leaves was increased by the treatment with abscisic acid and abiotic stresses such as cold, heat and high-salinity (NaCl). The motif search of the 5'-flanking sequence of the replacement histone H3 gene revealed the presence of several potential cis-acting elements that could respond to the above-mentioned abiotic stresses. In addition to defence-related elements, we also found type I and II-/III-like elements, which are highly conserved motifs in the 5'-regulatory sequence of plant histone genes that are expressed specifically during the S-phase. Experiments using transgenic Italian ryegrass plants proved that the isolated 5'-flanking sequence of the replacement histone H3 gene, which was fused to a beta-glucuronidase reporter gene, was fully functional for inducing gene expression under various abiotic stress conditions.