Differential Expression of Serine/Threonine Protein Phosphatase Type-2C Under Drought Stress in Maize

Differential display reverse transcription polymerase chain reaction was used to study the messenger RNA differential expression of a drought tolerant inbred line '81565' under drought stress and well-watered control. Fragments of MD1, MD2, and MD3 were found to be differentially expressed under drought stress. While the expression of MD1 and MD2 was down-regulated, the expression of MD3 was up-regulated. Sequence analysis of the three fragments revealed that MD1 shared 97% nucleotide sequence identity with maize chloroplast matK, a gene encoding RNA maturase involved in group II intron splicing of RNA transcript; MD2 had 99% identity with PP2C, a gene encoding serine/threonine phosphorylase 2C in resurrection grass Sporobolus stapfianus; and MD3 exhibited 99% sequence identity with a rice gene encoding metacaspase, an arginine/lysine-specific cysteine protease. Based on MD2 fragment sequence, a full-length complementary DNA of 1,731 bp was isolated. An open reading frame of 1,167 bp was found and predicted to encode a protein of 388 amino acids, containing the catalytic domain and conserved residues of serine/threonine protein phosphatase 2C. This open reading frame was identified as a new member of the PP2C gene family in maize and designated as ZmPP2Ca. The differential expression of ZmPP2Ca and enzyme activity of PP2C were also investigated in three drought-tolerant and two sensitive maize inbred lines under drought stress and well-watered (control) conditions by real-time fluorescence quantitative PCR and a non-radioactive labeled method, respectively. Down-regulation of the ZmPP2Ca transcript was observed in all three drought tolerant lines, whereas transcript levels were up-regulated in the two sensitive lines under drought stress. In light of the importance of protein kinases in signal transduction pathways, it is proposed that ZmPP2Ca may play a role in the signal transduction of maize in response to drought stress.