PHYTOCHROME-A, PHYTOCHROME-B AND OTHER PHYTOCHROME(S) REGULATE ATHB-2GENE-EXPRESSION IN ETIOLATED AND GREEN ARABIDOPSIS PLANTS

The expression of the Arabidopsis ATHB-2 gene is light-regulated both in seedlings and in adult plants, The gene is expressed at high levels in rapidly elongating etiolated seedlings and is down-regulated by a pulse of red light (R) through the action of a phytochrome other than phytochrome A or B, or by a pulse of far-red light (FR) through the ac tion of phytochrome A, In green plants, the expression of the ATHB-2 g ene is rapidly and strongly enhanced by lowering the R:FR ratio percei ved by a phytochrome other than A or B, Returning the plant to a high R:FR ratio results in an equally rapid decrease of the ATHB-2 mRNA, Co nsistently, plants overproducing ATHB-2 show developmental phenotypes characteristic of plants grown in low R:FR: elongated petioles, reduce d leaf area, early flowering, and reduced number of rosette leaves, Ta ken together, the data strongly suggest a direct involvement of ATHB-2 in light-regulated growth phenomena throughout Arabidopsis developmen t.