Expression of a novel-type small proline-rich protein gene of alfalfa is induced by 2,4-dichlorophenoxiacetic acid in dedifferentiated callus cells.

摘要

Differential screening of a cDNA library of 2,4-D-treated Medicago sativa callus tissues resulted in the isolation of a 571 bp cDNA clone (MsPRP5) coding for a proline-rich protein (84 amino acids) with a specific repeat unit of TPVLPPRK/RGRPPPVPP.In addition, a characteristic amino acid block (PPVYK), previously found in other proline-rich proteins, also occurred in the C-terminal region of MsPRP5. At the N-terminal, a signal peptide similar to leader sequences of extracellular proteins was predicted. According to northern analysis, the corresponding gene was not expressed or was weakly expressed in differentiated vegetative organs and somatic embryos. The accumulation of MsPRP5 mRNA was auxin concentration-dependent in dedifferentiated callus tissue. An increase in the amount of steady-state mRNA was detected 20 min after auxin shock (100 鍹 2,4-D). Maximum expression was observed at 24-48 h in the presence of 2,4-D. Elevated expression occurred in cells recovering after heat shock and wounding stress. In synchronized cells, the transcript level of MsPRP5 fluctuated during cell cycle progression, with peaks in G1/S phase cells. Considering the structural features and expression properties of MsPRP5, it is suggested that this clone may represents a new type of proline-rich protein gene which responds to hormonal shock and some other stresses. Nucleotide sequence data have been submitted to the EMBL/GenBank/DDBJ databases under the accession number X99099.