Expression analysis of KDEL-CysEPs programmed cell death markers during reproduction in Arabidopsis

CEP cell death markers. Programmed cell death (PCD) is essential for proper plant growth and development. Plant-specific papain-type KDEL-tailed cysteine endopeptidases (KDEL-CysEPs or CEPs) have been shown to be involved in PCD during vegetative development as executors for the last step in the process. The Arabidopsis genome encodes three KDEL-CysEPs: AtCEP1, AtCEP2 and AtCEP3. With the help of fluorescent fusion reporter lines, we report here a detailed expression analysis of KDEL-CysEP (pro)proteins during reproductive processes, including flower organ and germline development, fertilization and seed development. AtCEP1 is highly expressed in different reproductive tissues including nucellus cells of mature ovule and the connecting edge of anther and filament. After fertilization, AtCEP1 marks integument cell layers of the seeds coat as well as suspensor and columella cells of the developing embryo. Promoter activity of AtCEP2 is detected in the style of immature and mature pistils, in other floral organs including anther, sepal and petal. AtCEP2 mainly localizes to parenchyma cells next to xylem vessels. Although there is no experimental evidence to demonstrate that KDEL-CysEPs are involved in PCD during fertilization, the expression pattern of AtCEPs, which were previously shown to represent cell death markers during vegetative development, opens up new avenues to investigate PCD in plant reproduction.