Abscisic acid and hydrogen peroxide induce a novel maize group C MAP kinase gene, ZmMPK7, which is responsible for the removal of reactive oxygen species.

Mitogen-activated protein kinase (MAPK) cascades are involved in biotic and abiotic stress responses. In plants, MAPKs are classified into four groups, designated A-D. Information about group C MAPKs is limited, and, in particular, no data from maize are available. In this article, we isolated a novel group C MAPK gene, ZmMPK7, from Zea mays. Exogenous abscisic acid (ABA) and hydrogen peroxide (H(2)O(2)) induced calcium-dependant transcription of ZmMPK7. Induction of this gene in response to ABA was blocked by several reactive oxygen species (ROS) manipulators such as imidazole, Tiron, and dimethylthiourea (DMTU). This result indicates that endogenous H(2)O(2) may be required for ZmMPK7-mediated ABA signaling. Expression of ZmMPK7 in Nicotonia tobaccum caused less H(2)O(2) to accumulate and alleviated ROS-mediated injuries following submission of the plants to osmotic stress. The enhanced total peroxidase (POD) activity in transgenic tobacco plants may contribute to removal of ROS. Finally, we have shown that the ZmMPK7 protein localizes in the nucleus. These results broaden our knowledge regarding plant group C MAPK activity in response to stress signals.

Expression of MaMAPK gene in seedlings of Malus L. under water stress.

Seedlings of three species of Malus were used to study the expression of mitogen-activated protein kinase (MAPK) in response to water stress: Malus hupehensis, a drought-sensitive species; Malus sieversii, a drought-tolerant species; and Malus micromalus, a middle type. Results showed that Malus MAPK (MaMAPK, GenBank accession No. AF435805) was expressed in both roots and leaves of seedlings of the three Malus species treated with 20% polyethylene glycol for different time periods. Expression levels peaked at 1.5 h after treatment with polyethylene glycol, then decreased to their lowest levels. Liquid kinase assays indicated that the dynamic changes of MAPK activity were very similar to those of the relative expression of MaMAPK mRNA. However, the peak of the former occurred slightly behind the latter. It was noticed that, although the kinase activity decreased after the peak, it was still higher than that of the control during the whole time period. These results suggested that MaMAPK was regulated not only by water stress at the transcription level, but also by phosphorylation and dephosphorylation at the protein level. In addition, of these three apple species, the highest MAPK activity and MaMAPK expression level was found in M. sieversii, followed by M. micromalus and M. hupehensis, suggesting that MAPK might be correlated with drought tolerance in these three species. The different expression levels might be one of the molecular mechanisms of the different drought tolerances in Malus.

[Cloning and expression characteristics of protein phosphatase gene ZmPP2C of Zea mays roots].

According to the conserved motifs of plant protein phosphatase 2C gene, degenerate oligonucleotides were designed. A full cDNA sequence of PP2C gene from Zea mays L. roots was cloned by RT-PCR. It was named ZmPP2C and had 936 bp. Southern blot showed that the ZmPP2C gene was a low copy in the Zea mays genome, and there was a small PP2C gene family. Northern blot showed that the expression of ZmPP2C gene was significantly different among Zea mays tissues. Zea mays roots treated with CaCl(2), MgCl(2), PEG, EGTA, and ABA for 24 h, the ZmPP2C expression increased only by CaCl(2) treatment. It showed the transcription of ZmPP2C gene was induced by Ca(2+), or in a Ca(2+)-dependent manner.