Complete blockage of the mevalonate pathway results in male gametophyte lethality.
Plants have two isoprenoid biosynthetic pathways: the cytosolic mevalonate (MVA) pathway and the plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. Since the discovery of the MEP pathway, possible metabolic cross-talk between these pathways has prompted intense research. Although many studies have shown the existence of such cross-talk using feeding experiments, it remains to be determined if native cross-talk, rather than exogenously applied metabolites, can compensate for complete blockage of the MVA pathway. Previously, Arabidopsis mutants for HMG1 and HMG2 encoding HMG-CoA reductase (HMGR) were isolated. Although it was shown that HMGR1 is a functional HMGR, the enzyme activity of HMGR2 has not been confirmed. It is demonstrated here that HMG2 encodes a functional reductase with similar activity to HMGR1, using enzyme assays and complementation experiments. To estimate the contribution of native cross-talk, an attempt was made to block the MVA pathway by making double mutants lacking both HMG1 and HMG2, but no double homozygotes were detected in the progeny of self-pollinated HMG1/hmg1 hmg2/hmg2 plants. hmg1 hmg2 male gametophytes appeared to be lethal based on crossing experiments, and microscopy indicated that approximately 50% of the microspores from the HMG1/hmg1 hmg2/hmg2 plant appeared shrunken and exhibited poorly defined endoplasmic reticulum membranes. In situ hybridization showed that HMG1 transcripts were expressed in both the tapetum and microspores, while HMG2 mRNA appeared only in microspores. It is concluded that native cross-talk from the plastid cannot compensate for complete blockage of the MVA pathway, at least during male gametophyte development, because either HMG1 or HMG2 is required for male gametophyte development.
RIKEN Plant Science Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan.
Masashi
M
Suzuki
Shoko
S
Nakagawa
Yukiko
Y
Kamide
Keiko
K
Kobayashi
Kiyoshi
K
Ohyama
Hiromi
H
Hashinokuchi
Reiko
R
Kiuchi
Kazuki
K
Saito
Toshiya
T
Muranaka
Noriko
N
Nagata
D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D053898:Biosynthetic Pathways; D004896:Erythritol / Q000031:analogs & derivatives / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005854:Germ Cells / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics / Q000378:metabolism*; D008798:Mevalonic Acid / Q000378:metabolism*; D013045:Species Specificity; D013403:Sugar Phosphates / Q000378:metabolism
C114232:2-C-methylerythritol 4-phosphate; D029681:Arabidopsis Proteins; D013403:Sugar Phosphates; D006903:Hydroxymethylglutaryl CoA Reductases; D004896:Erythritol; D008798:Mevalonic Acid