ZEN1 Is a Key Enzyme in the Degradation of Nuclear DNA during Programmed Cell Death of Tracheary Elements

Abstract

Tracheary elements (TEs) have a unique cell death program in which the rapid collapse of the vacuole triggers the beginning of nuclear degradation. Although various nucleases are known to function in nuclear DNA degradation in animal apoptosis, it is unclear what hydrolase is involved in nuclear degradation in plants. In this study, we demonstrated that an S1-type nuclease, Zinnia endonuclease 1 (ZEN1), functions directly in nuclear DNA degradation during programmed cell death (PCD) of TEs. In-gel DNase assay demonstrated the presence of a 24-kD Ca 2 ؉ /Mg 2 ؉ -dependent nuclease and a 40-kD Zn 2 ؉ -dependent nuclease as well as ZEN1 in 60-h-cultured cells that included differentiating TEs. Such cell extracts possessed the ability to degrade the nuclear DNA isolated from Zinnia elegans cells in the presence of Zn 2 ؉ , and its activity was suppressed by an anti-ZEN1 antibody, indicating that ZEN1 is a central DNase responsible for nuclear DNA degradation. The introduction of the antisense ZEN1 gene into Zinnia cells cultured for 40 h specifically suppressed the degradation of nuclear DNA in TEs undergoing PCD but did not affect vacuole collapse. Based on these results, a common mechanism between animal and plant PCD is discussed.

Coordinate involvement of cysteine protease and nuclease in the executive phase of plant apoptosis

“…However, only limited information is available about plant effectors, especially those involved in the executive phase of plant PCD. Several lines of evidence implicate cysteine proteases and nucleases in the commitment to plant PCD during oxidative stress- [5] and mannose-induced cell death [22], tracheary element differentiation [23] and the HR [24]. However, it is not yet clear whether those enzymes are directly involved in the executive phase in plant PCD or in upstream signaling pathways.…”

Formation of plant tracheary elements in vitro – a review

“…Demura et al (2002) constructed a comprehensive profile of gene expression in an in vitro Zinnia culture system to gather fundamental information about the gene regulation underlying the differentiation of plant cells. Together, Ito and Fukuda (2002) demonstrated that Zinnia elegans endonuclease 1 (ZEN1) is a key enzyme in the degradation of nuclear DNA during programmed cell death of TEs. Reactive oxygen species, such as hydrogen peroxide, are important signalling compounds in various cell death processes in plants.…”

“…The results suggested that brassinosteroids biosynthesis during TE differentiation may be regulated by the coordinated regulation of biosynthesis of sterols and brassinosteroids. The team of Ito and Fukuda (2002) demonstrated that an S1-type nuclease, Zinnia endonuclease 1, is a central DNase responsible for nuclear DNA degradation during programmed cell death of Zinnia TEs. Later, Ito et al (2006) reported that a dodeca-CLE peptide suppresses Zinnia TE differentiation.…”

“…Three common methods used to transform xylogenic lines are biolistic particle delivery (Ito and Fukuda 2002;Möller et al 2003;Wagner et al 2012), Agrobacterium tumefaciens-mediated transformation (Pyo et al 2007;Pesquet et al 2010;Ohashi-Ito et al 2010) and electroporation (Endo et al 2008).…”

“…Ito and Fukuda (2002) achieved the transformation of cultured Z. elegans cells with the Z. elegans endonuclease 1 (ZEN1) gene using a particle bombardment method. Pinus radiata xylogenic cell cultures can be transformed biolistically using a particle gun and subsequently used for testing of genes related to cell differentiation and cell-wall formation (Möller et al 2003;Wagner et al 2012).…”