OVEREXPRESSED PHYTOCHROME-C HAS SIMILAR PHOTOSENSORY SPECIFICITY TO PHYTOCHROME-B BUT A DISTINCTIVE CAPACITY TO ENHANCE PRIMARY LEAF EXPANSION

Phytochrome C (phyC) is a low-abundance member of the five-membered ph ytochrome family of photoreceptors in Arabidopsis. Towards developing an understanding of the photosensory and physiological functions of ph yC, transgenic Arabidopsis plants were generated that overexpress cDNA -encoded phyC and seedling responses to continuous white, red, or far- red light (Wc, Rc or FRc, respectively) were examined. Transgenic seed lings overexpressing phyC displayed enhanced inhibition of hypocotyl e longation in Rc, but were unchanged in responsiveness to FRc relative to wild-type. These data indicate that phyC has photosensory specifici ty that is similar to that of phyB and thus distinct from that of phyA . phyC overexpressors with levels only 3 to 4 times the level of endog enous phyC exhibited enhanced primary leaf expansion in Wc. This is in contrast to phyA or phyB overexpressors which respectively have level s that are 500- and 100-fold that of overexpressed phyC but showed no enhancement of primary leaf expansion. Therefore, phyC may have some p hysiological roles that are different to those of phyA and phyB in the control of seedling responses to light signals.