B. Forster et al., HERBICIDE RESISTANCE AND GROWTH OF D1 ALA(251) MUTANTS IN CHLAMYDOMONAS, Zeitschrift fur Naturforschung. C, A journal of biosciences, 52(9-10), 1997, pp. 654-664
We elucidated the effects of substituting seven amino acids for Ala at
residue 251 of the Chlamydomonas reinhardtii D1 protein on herbicide
resistance and photoautotrophic growth. Ala(251) has been suggested to
play a key role in the structural integrity and function of the strom
al loop between transmembrane helices IV and V of D1 and has previousl
y been shown to affect resistance to ''classical'' PSII specific herbi
cides. Sensitive and rapid microtiter assays were employed to compare
herbicide resistance and photoautotrophic growth in the various mutant
s. Substitution of Ala(251) by Ile, Leu or Val conferred resistance to
the PSTI herbicides atrazine, bromacil and metribuzin but not to DCMU
and impaired photoautotrophic growth in high and low light. Compared
to an otherwise isogenic wildtype strain, the Ile and Val mutants exhi
bited nearly identical levels of herbicide resistance and reduced grow
th while the Leu mutant had even slower growth and higher levels of he
rbicide resistance. In contrast Cvs, Pro, Ser and Gly mutants were phe
notypically indistinguishable from wildtype in terms of herbicide sens
itivity and photoautotrophic doubling times. Collectively, the seven A
la(251) mutations differed markedly from an Ala mutant (dr-1) at the w
ell characterized Ser(264) D1 residue in terms of herbicide resistance
and photoautotrophic growth.