Unfavourable environment brings many kinds of stresses to plants. To survive such stresses, efficient resistance is required for the plants. Multifunctional genes enable the cross-talk among the various abiotic stress resistance systems. This paper reviews the action mechanisms of multifunctional genes. These genes can be classified into three groups: genes encoding diverse proteins through mRNA splicing (e.g. AOX in rice); genes like BADH, P5CS and HAV that control drought, salinity, osmotic and heat stress resistance; and a gene family, for example AQP, controlling transport of many compounds including water and nutrients. These genes participate in signal sensing and transduction, transcriptional regulation and functional gene activation during stress resistance induction. Furthermore, it should be noted that, under abiotic stresses, the regulation cascades are mutually interdependent and there also exists a close correlation between those cascades and normal plant growth and development.

The NADP-dependent malic enzyme (NADP-ME; EC1.1.1.40) found in many metabolic pathways catalyzes the oxidative decarboxylation of L-malate, producing pyruvate, CO 2 and NADPH. The NADP-MEs have been well studied in C4 plants but not well in C3 plants. In this study, we identified the NADP-ME isoforms from hexaploid wheat (Triticum aestivum L). Two different NADP-ME transcripts were first identified in this C3 plant. The first is named TaNADP-ME1 [NCBI: EU170134] and encodes a putative plastidic isoform, while the second is named TaNADP-ME2 [NCBI: EU082065] and encodes a cytosolic counterpart. Sequence alignment shows that the two NADP-ME isoforms share an identity of 73.26% in whole amino acids and 64.08% in nucleotide sequences. The phylogenetic analysis deciphers the two NADP-MEs as belonging to the monocots (Group II), which closely resemble OschlME6 and OscytME2, respectively. Tissue-specific analyses indicate that the two NADP-ME genes are both expressed in root, stem and leaf, and that TaNADP-ME1 is a leaf-abundant isoform. Semi-quantitative RT-PCR analysis show that the two NADP-ME transcripts in wheat leaves respond differently to low temperature, salt, dark and drought stresses stimuli and to exogenous abscisic acid (ABA) and salicylic acid (SA). Our results demonstrate that exogenous hormones (ABA and SA), as well as salt, low temperature, dark and drought stresses can regulate the expressions of TaNADP-ME1 and TaNADP-ME2 in wheat. This indicates that the two NADP-ME genes may play an important role in the response of wheat to ABA, SA, low temperature, salt, dark and drought stress.

The objective of this study was to examine the effects of different abiotic stresses on the activity of an NADPdependent malic enzyme (NADP-ME) and the corresponding gene transcription in the leaves of the hexaploid wheat (Triticum aestivum L.) The activity of the NADP-ME enzyme was increased by water stress (20 % polyethylene glycol 6000), low temperature (4 °C), darkness, salinity (200 mM NaCl), abscisic acid and salicylic acid. The transcription of the TaNADP-ME1 gene decreased in response to all of the stresses except darkness and NaCl. In addition, the transcription of TaNADP-ME2 was down-regulated by all of the tested treatments and could not be detected under dark stress.