A LEAF-SPECIFIC GENE STIMULATED BY LIGHT DURING WHEAT ACCLIMATION TOLOW TEMPERATURE

We report here the identification and characterization of a new leaf-s pecific light-stimulated gene induced during cold acclimation of wheat . Sequence analysis revealed that the gene encodes a protein of 19 kDa with a pI of 8.8. This is a novel protein with a particular charge di stribution. The C-terminal half has a high propensity to form an alpha -helix and contains all the acidic amino acids with a net negative cha rge of -7. On the other hand, the N-terminal half is rich in proline, lysine and arginine with a net positive charge of +10. These propertie s are commonly found in several transcription factors. The protein is also rich in alanine (21 %), is hydrophilic but not boiling soluble in contrast to other alanine-rich proteins. During low temperature expos ure, the corresponding mRNA accumulates rapidly in the leaf and remain s at a constant level in two tolerant cultivars used. However, in a le ss tolerant cultivar, the mRNA level declines despite maintaining the plants at 4-degrees-C. Southern blot analysis indicates that the diffe rential expression in the less tolerant genotype is not due to a diffe rent genomic organization or gene copy number. The mRNA was specifical ly localized in leaf tissues and increased several-fold during the gre ening at 4-degrees-C. Furthermore, this gene is not induced in callus cultures acclimated in the absence or presence of light. This suggests that the full expression of this gene is dependent on organized leaf tissue. The expression of this gene was not affected by ABA, drought, heat shock, salinity, wounding or anaerobiosis, demonstrating that it is specifically induced by low temperature. The Wcs19 mRNA is preferen tially expressed in tolerant Gramineae species.