IDENTIFICATION OF PHYTOCHROME-B AMINO-ACID-RESIDUES MUTATED IN 3 NEW PHYB MUTANTS OF ARABIDOPSIS-THALIANA

The growth and development of plants is regulated by light via the act ion of photoreceptors which are responsive to the red/far-red, blue an d UV regions of the spectrum. Phytochrome B (the apoprotein of which i s encoded by the PHYB gene) is one of the red/far-red absorbing photor eceptors active in this process, In this paper, the isolation and char acterization of three new EMS-induced mutations of Arabidopsis which c onfer phytochrome B deficiency are described. Complementation analysis showed that these mutations (phyB-101, phyB-102 and phyB-104) were al lelic with PHYB, DNA sequence analysis showed that all three mutants c ontain nucleotide substitutions in the PHYB gene sequence. phyB-101 ca rries a nucleotide substitution within the second exon of the PHYB gen e. This G-to-A substitution is a missense mutation that converts a glu tamate residue at position 812 of the phytochrome B apoprotein to a ly sine residue, phyB-102, another missense mutant, carries a C-to-T subs titution which converts a serine residue at position 349 of the phytoc hrome B apoprotein to a phenylalanine residue. phyB-104 carries a prem ature stop codon as a result of a G-to-A mutation 1190 bp down-stream of the ATG start codon of the PHYB sequence, The missense mutations in phyB-101 and phyB-102 cause significant alterations in the predicted secondary structure of their respective mutant polypeptides, and ident ify amino acid residues playing crucial roles in phytochrome B functio n, assembly or stability.