The proteasome is responsible for caspase‐3‐like activity during xylem development

Abstract

Summary Xylem development is a process of xylem cell terminal differentiation that includes initial cell division, cell expansion, secondary cell wall formation and programmed cell death (PCD). PCD in plants and apoptosis in animals share many common characteristics. Caspase‐3, which displays Asp‐Glu‐Val‐Asp (DEVD) specificity, is a crucial executioner during animal cells apoptosis. Although a gene orthologous to caspase‐3 is absent in plants, caspase‐3‐like activity is involved in many cases of PCD and developmental processes. However, there is no direct evidence that caspase‐3‐like activity exists in xylem cell death. In this study, we showed that caspase‐3‐like activity is present and is associated with secondary xylem development in Populus tomentosa. The protease responsible for the caspase‐3‐like activity was purified from poplar secondary xylem using hydrophobic interaction chromatography (HIC), Q anion exchange chromatography and gel filtration chromatography. After identification by liquid chromatography‐tandem mass spectrometry (LC‐MS/MS), it was revealed that the 20S proteasome (20SP) was responsible for the caspase‐3‐like activity in secondary xylem development. In poplar 20SP, there are seven α subunits encoded by 12 genes and seven β subunits encoded by 12 genes. Pharmacological assays showed that Ac‐DEVD‐CHO, a caspase‐3 inhibitor, suppressed xylem differentiation in the veins of Arabidopsis cotyledons. Furthermore, clasto‐lactacystin β‐lactone, a proteasome inhibitor, inhibited PCD of tracheary element in a VND6‐induced Arabidopsis xylogenic culture. In conclusion, the 20S proteasome is responsible for caspase‐3‐like activity and is involved in xylem development.

The Cysteine Protease CEP1, a Key Executor Involved in Tapetal Programmed Cell Death, Regulates Pollen Development in Arabidopsis

“…The papain-like cysteine proteases are the most thoroughly investigated family among cysteine proteases. Many of these are typically active in acid pH environments including the apoplast, vacuole, and lysosomes (Trobacher et al, 2006), and many are implicated in a variety of PCD events in various tissues, including xylogenesis (Han et al, 2012), leaf and flower senescence (Chen et al, 2002;Eason et al, 2002;Rabiza-Świder et al, 2003;Senatore et al, 2009), and seed development and germination (Wan et al, 2002;Greenwood et al, 2005).…”

Transcriptome analysis provides insights into wood formation during larch tree aging

“…Programmed cell death is the last step in xylem development, and much is known about its molecular processes (Escamez and Tuominen 2014;Han et al 2012). When wood is forming actively and more xylem cells are developing, more cells are dying at the same time.…”

Comparative study of salt stress-induced physiological and molecular responses in tomato (Solanum lycopersicum L.)

“…Although, their homologs have not been found in plant genomes, some plant proteases have caspase-like activity including Cys proteases and proteasome catalytic subunits (Han et al, 2012).…”

“…Caspase-3 is the main effector in the processing cascade (Tawa et al, 2004). Caspase homologues have not been found in plant genomes but plants exhibit caspase-like-protease activity (cleaving after Asp residues) (Han et al, 2012). For example, VPE has caspase-1 activity and is required for virus-induced PCD in tobacco (Hatsugai et al, 2004), whereas the β1 catalytic subunit of the 20S proteasome has caspase-3 activity that is required for PCD triggered by Pseudomonas syringae pv.…”

“…RD21 is located in pre-vacuole endoplasmic reticulum (ER) bodies and in the vacuole (Hatsugai et al, 2009). Furthermore aleurains in leaf and flower tissue, and a XBCP3-like protease in the root tissue play critical roles at early stages of cell death (Funk et al, 2002;Asp et al, 2004, Eason et al, 2005Avci et al, 2008;Han et al 2012).…”