Genome-wide analysis of the polyamine oxidase gene family in Citrus sinensis
Wei Wang, Jihong Liu^*

College of Horticulture & Foresty Science, Huazhong Agricultural University, Wuhan, 430070.
^*Corresponding author: Tel: (+8627) 87282399; Fax:  (+8627) 87280016; E-mail: liujihong@mail.hzau.edu.cn

Abstract
Polyamine oxidases (PAOs) are FAD-dependent enzymes involved in polyamine catabolism. In plants, increasing evidence supports that PAOs play an essential role in abiotic and biotc stress response. In this study, we investigated 6 putative polyamine oxidases genes from Citrus sinensis genome and compared them with those from Arabidopsis. We provide a comprehensive overview of the polyamine oxidases genes family in citrus sinensis (CsPAOs), describing the gene structure, promoter cis-regulatory elements, phylogeny, genome localization, Organ-specific expression and gene expression patterns under stress and hormone treatment. Cis-regulatory elements prediction showed that 175 putative cis elements more than 6 bp in length were identified in the 1.5 kb of upstream promoter regions, including stress response and hormone response elements. Gene expression patterns analysis found that most of these polyamine oxidase genes were induced by low temperature, salt, drought and ABA treatment. All the CsPAOs were positively induced except for CsPAO6 by low temperature. The transcript level of CsPAO6 decreased after cold treatment. With respect to NaCl and drought treatment, the expression levels of most of the CsPAOs significantly decreased. These expression pattens under ABA treatment were similar to those under NaCl and drought treatment, and most of the CsPAOs were negatively induced by ABA, suggesting that ABA may be involved in polyamines catabolism.

Key words: Citrus sinensis; polyamine oxidase; abiotic stress;abscisic acid; stress response; gene expression