| Phospholipase D (PLD),which hydrolyzes phospholipids to produce phosphatidic acid (PA) and a free head group, has been detected in bacteria, fungi, plants, and animals. In plant, PLD as well as its product PA play key roles in numerous cellular processes including stress responses, hormone effects, membrane vesicle trafficking and cytoskeleton rearrangements. To elucidate the physiological functions of PLD, an Arabidopsis thaliana cDNA encoding AtPLDζ2, was isolated and functional characterized.AtPLDζ2 was constitutively expressed in various tissues and induced by auxin, and phenotypic analysis on the AtPLDζ2 defected mutant, atpldζ2, and transgenic plants deficiency of AtPLDζ2 showed they were insensitive to auxin, and also have reduced root gravitropism and suppressed auxin-dependent hypocotyls elongation under high temperature (29oC); while the transgenic seedlings overexpressing AtPLDζ2 showed opposite responses, suggesting AtPLDζ2 positively mediates auxin signaling. Further studies using seedlings containing DR5-GUS construct and on the expression profiles of early auxin responsive genes indicated that AtPLDζ2, or PA, stimulated auxin responses. Observations on the internalization of membrane selective dyes FM4-64 showed the suppressed vesicle trafficking under deficiency of AtPLDζ2 or by treatment with PLD specific inhibitor 1-butanol, whereas which was obviously enhanced under PA or enhanced AtPLDζ2. 1-butanol has no effects on the localization of PIN1 and PIN2, but blocks the inhibition of BFA on PIN1 and PIN2 cycling. These results suggest that AtPLDζ2 and its product PA, stimulates auxin responses via accelerating vesicle trafficking.
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