Plant Physiol, January 2000, Vol. 122, pp. 49-56
Antisense HEMA1 RNA Expression Inhibits Heme and
Chlorophyll Biosynthesis in Arabidopsis1
A. Madan
Kumar and
Dieter
Söll*
Department of Molecular Biophysics and Biochemistry (A.M.K., D.S.)
and Department of Molecular, Cellular and Developmental Biology (D.S.),
Yale University, New Haven, Connecticut 06520-8114.
5-Aminolevulinic acid (ALA) is a
precursor in the biosynthesis of tetrapyrroles including chlorophylls
and heme. The formation of ALA involves two enzymatic steps which take
place in the chloroplast in plants. The first enzyme, glutamyl-tRNA
reductase, and the second enzyme,
glutamate-1-semialdehyde-2,1-aminomutase, are encoded by the nuclear
HEMA and GSA genes, respectively. To
assess the significance of the HEMA gene for chlorophyll
and heme synthesis, transgenic Arabidopsis plants that expressed
antisense HEMA1 mRNA from the constitutive cauliflower
mosaic virus 35S promoter were generated. These plants exhibited
varying degrees of chlorophyll deficiency, ranging from patchy yellow
to total yellow. Analysis indicated that these plants had decreased
levels of chlorophyll, non-covalently bound hemes, and ALA; their
levels were proportional to the level of glutamyl-tRNA reductase
expression and were inversely related to the levels of antisense
HEMA transcripts. Plants that lacked chlorophyll failed
to survive under normal growth conditions, indicating that
HEMA gene expression is essential for growth.
1
This work was supported by the Department of
Energy (grant no. DE-FG02-87ER13734).
*
Corresponding author; e-mail soll{at}trna.chem.yale.edu; fax
203-432-6202.
© 2000 American Society of Plant Physiologists
