The expression of Arabidopsis auxin response factor 8 (ARF8) can be promoted by light and is involved in light signaling. However, little is known about the pathway and mechanismunder lying signal transduction fromphotoreceptors to ARF8. Semi-quantitative RT-PCR analys is revealed that mutation of PhyA elevated the expression of ARF8, but that of PhyB, Cry1 or Cry2 did not change the expression of ARF8 markedly. GUS staining, semi-quantitative RT-PCR and real- time RT-PCR were used to analyze how PhyA systemic ally aff ected the expression of ARF8. GUS staining in related GUS lines suggested that mutation of PhyA affects the mRNA expression of ARF8 in an organ-spec ific manner. In cotyledons , PARF8:GUS showed weak staining but phyA-209 PARF8:GUS showed strong staining. In the shoot apical mer istem, hypocotyl and root tip, phyA-209 PARF8:GUS showed weaker staining than did PARF8:GUS. The same expression patterns of ARF8 resulting from disruption of PhyA were observed in dark, white light and f ar-red light conditions. This expression pattern was further confirmed by semi-quantitative and real-time RTPCR analysis. However, the expression of PhyA in arf8-1 was almost the same as in the wild type, which suggests that disruption of ARF8 does not change the expression of PhyA. Our results suggest that ARF8 acts downs tream of PhyA in far- red light signaling.