CgSL2, an S-like RNase gene in 'Zigui shatian' pummelo (Citrus grandis Osbeck), is involved in ovary senescence

'Zigui shatian' pummelo (Citrus grandis Osbeck) is one nature mutant from 'Shatian' pummelo, which showed self-compatibility, because self-pollen tubes were not arrested in the style, moreover abnormal post-zygotic development in ovary caused seed abortion in the cultivar. Herein we constructed a cDNA library from flowers of 'Zigui shatian' pummelo and identified one RNase gene fragment. The full length of cDNA sequence of this gene, with an open reading frame of 834 bp, was isolated by 5'-RACE method. The gene, named as CgSL2, contained five conserved regions and two histidine residues essential for RNase activity. Phylogenetic analysis indicated that CgSL2 was mostly similar to AhSL28, an S-like RNase from Antirrhinum. Southern hybridization verified CgSL2 existed in the genome as multiple copies. qRT-PCR and RT-PCR analysis showed that the expression of CgSL2 was not tissue-specific. The expression of CgSL2 was down-regulated during senescence of stem, petal, style and stamen, whereas up-regulated during ovary senescence. Further in situ hybridization of CgSL2 in the ovary during the balloon stage to anthesis stage also showed that it dramatically increased in mature flower, consistent with qRT-PCR and RT-PCR results. These findings suggested that CgSL2 might play an important role during ovary senescence.