Involvement of a MAP kinase, ZmMPK5, in senescence and recovery from low-temperature stress in maize.
Four species of protein kinase were identified in senescent maize leaves using a gel assay for kinase activity with myelin basic protein (MBP) as the substrate. Most of these kinases were also found in healthy green leaves that had been exposed to low-temperature stress (5 degrees C) and then returned to 25 degrees C. A 41-kDa protein was activated in senescent leaves, whereas a 45-kDa protein was activated 3 h after up-shift from 5 degrees C to 25 degrees C as well as in senescent leaves. A 39-kDa protein was activated by cold stress. The other two proteins, of 35 kDa and 52 kDa, constitutively phosphorylated MBP during senescence and temperature up-shift. Judging from their molecular masses, cation requirements and substrate specificities, it seemed likely that the 39-kDa, 41-kDa and 45-kDa proteins represented mitogen-activated protein kinases (MAPKs). Subsequently two MAPK cDNAs were isolated from a cDNA library constructed using mRNAs from senescent leaves. Northern analysis showed that the transcript corresponding to one of the cDNAs, designated ZmMPK5, accumulated in healthy leaves 3 h after the up-shift to 25 degrees C as well as in senescent leaves, suggesting that the 45-kDa protein kinase is encoded by ZmMPK5. Western analysis using an antiserum against the C-terminal region of ZmMPK5 showed that the level of the ZmMPK5 protein increased in senescent leaves. These results indicate that a 45-kDa MAPK is involved in the process of senescence and in recovery from low-temperature stress in maize plants.
Berberich
T
T
Botanisches Institut, Goethe-Universität, Frankfurt am Main, Germany.
Sano
H
H
Kusano
T
T
D000595:Amino Acid Sequence; D016922:Cellular Senescence; D003080:Cold Temperature; D004789:Enzyme Activation; D015723:Gene Library; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000201:enzymology; D010940:Plant Proteins; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D003313:Zea mays / Q000502:physiology*
D010940:Plant Proteins; D020928:Mitogen-Activated Protein Kinases; C402117:ZmMPK5