A DELETION IN THE PHYD GENE OF THE ARABIDOPSIS WASSILEWSKIJA ECOTYPE DEFINES A ROLE FOR PHYTOCHROME-D IN RED FAR-RED LIGHT SENSING/

The PHYD gene of the Wassilewskija (Ws) ecotype of Arabidopsis contain s a 14-bp deletion (the phyD-1 mutation) beginning at amino acid 29 of the reading frame, resulting in translation termination at a nonsense codon 138 nucleotides downstream of the deletion end point, Immunoblo t analyses showed that Ws lacks phyD but contains normal levels of phy A, phyB, and phyC. By backcrossing into the Ws and Landsberg erecta ge netic backgrounds, we constructed sibling pairs of PHYD+ and phyD-1 li nes and of phyB(-) PHYD+ and phyB(-) phyD(-) lines. Hypocotyl lengths after growth under white or red light increased sequentially in strain s that were B+D+, B+D-, B-D+, and B-D-. In the Ws genetic background, an increase in petiole length, a reduction in cotyledon area and in an thocyanin accumulation in seedling stems, a diminished effect of an en d-of-day pulse of far-red light on hypocotyl elongation, and a decreas e in the number of rosette leaves at the onset of flowering were also seen sequentially in these lines, Thus, phyD, which is similar to 80% identical in amino acid sequence to phyB, acts in conjunction with phy B in regulating many shade avoidance responses. The existence of the a pparently naturally occurring phyD-1 mutation indicates that phyD is n ot essential in some natural environments.