Our studies on pine hypocotyl cuttings and cuttings from hedged stock plants indicate that expression of the LPEAs is correlated with adventitious root formation. We transformed tobacco with the fusions of the coding regions of three of the LPEAs with the 35s constitutive promoter. While the phenotypes of most lines are normal, some lines had phenotypes that resembled plants with a decreased auxin response. These represent potential regulatory targets, as recent reports indicate that protein kinases are important for down-regulating the auxin response. We cloned and are analyzing the promoter of LPEA1.
Sequence analysis reveals several putative auxin-responsive elements.
In roots of transgenic tobacco plants containing the full promoter fused to the GUS reporter gene, GUS is expressed in the vascular tissue of developing primary and lateral roots. However, in plants containing a truncated promoter, GUS expression is observed in the epidermis and root hairs. Thus, the deleted portion of the promoter may contain both positive and negative regulatory elements that are tissue-specific and related to root development. Further experiments are underway to determine the temporal and spatial expression during adventitious root formation. We are screening for additional auxin-responsive genes using microarray technology.