The proteasome is responsible for caspase-3-like activity during xylem development.
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.
State Key Laboratory of Protein and Plant Gene Research, College of Life Sciences, Peking University, Beijing 100871, China.
Jia-Jia
JJ
Han
Wei
W
Lin
Yoshihisa
Y
Oda
Ke-Ming
KM
Cui
Hiroo
H
Fukuda
Xin-Qiang
XQ
He
D017209:Apoptosis; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D053148:Caspase 3 / Q000302:isolation & purification / Q000378:metabolism; D002454:Cell Differentiation; D002473:Cell Wall / Q000378:metabolism; D007783:Lactones / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000302:isolation & purification* / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism; D018547:Plant Stems / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D030821:Plants, Genetically Modified; D032107:Populus / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D046988:Proteasome Endopeptidase Complex / Q000302:isolation & purification* / Q000378:metabolism; D061988:Proteasome Inhibitors; D036226:Seedlings / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D052584:Xylem / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development
D007783:Lactones; D009842:Oligopeptides; D010940:Plant Proteins; D061988:Proteasome Inhibitors; C099158:acetyl-aspartyl-glutamyl-valyl-aspartal; C098869:clasto-lactacystin beta-lactone; D010447:Peptide Hydrolases; D053148:Caspase 3; D046988:Proteasome Endopeptidase Complex