Expression of a putative laccase gene, ZmLAC1, in maize primary roots under stress*

Laccases are multi-copper-containing glycoproteins and comprise a multi-gene family in plants. However, their physiological functions are still not well understood. We obtained sequence information for a putative laccase gene, ZmLAC1, from maize and studied ZmLAC1 expression in detail. The deduced ZmLAC1 protein was 70% identical to LpLAC5-4, a laccase from ryegrass. ZmLAC1 was expressed in leaves, stems and roots of maize seedlings. In unstressed maize primary roots, a higher ZmLAC1 transcript level was located in the basal region where cell elongation had ceased compared to the apical 5 mm of the roots where cells were rapidly dividing and elongating. A treatment with 300 mM NaCl resulted in a shortened root elongation zone (< 2 mm) and swelling in the apical 5 mm. Associated with the morphological change, the transcript level of ZmLACl was enhanced in the apical 5 mm, reaching a level similar to that in the basal region. Other abiotic stresses tested--such as 28.5% polyethylene glycol (PEG), which caused an inhibition of root elongation comparable to 300 mM NaCl--did not affect ZmLAC1 transcript level. Potential roles of ZmLAC1 in the roots responding to NaCl or other high concentration of salts are discussed.