Endonuclease genes up-regulated in tissues undergoing programmed cell death are expressed during male gametogenesis in barley

In the process of programmed cell death (PCD), a key role has been attributed to endonucleases capable to cleave nuclear DNA at internucleosomal sites. In barley (Hordeum vulgare L.), two such nucleases (Bnuc1 and BEN1) were individually identified in unrelated tissues. In the present work, we demonstrate that their genes are also expressed in immature anthers at different stages of pollen development. Further experiments carried out on RNA extracted from immature barley anthers led to discover a novel endonuclease gene, namely Bnuc2 (AJ311603 in the EMBL/GenBank/DDBJ databases), eventually found up-regulated at the tetrad stage. The protein encoded was found to conserve large sequence portions of Bnuc1 and BEN1 endonucleases, including the domain regions involved in secretion and DNA/RNA binding. A survey conducted on barley EST libraries showed that Bnuc2 and BEN1 mRNAs are jointly present also in the transcriptome of 20 DAP spike and that other endonuclease ESTs are co-expressed with Bnuc1 or BEN1 in tissues where PCD has been recorded. Therefore, it can be concluded that during the PCD process, a set of S1-type endonucleases is synthesised regardless of the tissue considered.