Complete blockage of the mevalonate pathway results in male gametophyte lethality

Abstract

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 ∼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.

Disruption of the 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) gene results in albino, dwarf and defects in trichome initiation and stomata closure in Arabidopsis

“…It was previously reported that the MVA pathway plays a more important role than the MEP pathway during reproductive development in Arabidopsis [62,63]. Another interesting phenomenon from our study is that the heterozygous dxr mutant plants set normal homozygous seeds, suggesting that, without the MEP pathway, the gametophytes, embryo sac or later-developed homozygous embryo can develop normally, consistent with the previous reports.…”

Sterol Methyl Oxidases Affect Embryo Development via Auxin-Associated Mechanisms

“…Plant sterols play important roles in reproductive developmental processes such as embryogenesis and male fertility (Clouse, 2002;Schaller, 2003;Suzuki et al, 2004Suzuki et al, , 2009). However, it has not been shown that sterols are required for endosperm development.…”

Identification of floral genes for sex determination in Calamus palustris Griff. by using suppression subtractive hybridization

“…A study of the FKP 1 mutant revealed that the HMGCS enzyme is important in the mevalonate pathway for developing the tapetumspecific organelle and the fertility of pollen (Ishiguro et al, 2010). A null allele of FKP 1 produced male gametophytes that were lethal before the elongation of the pollen tube, and its absence caused sterile male gametophytes (Suzuki et al, 2009). …”