Overexpression of CYP710A1 and CYP710A4 in transgenic Arabidopsis plants increases the level of stigmasterol at the expense of sitosterol

Abstract

Sitosterol and stigmasterol are major sterols in vascular plants. An altered stigmasterol:sitosterol ratio has been proposed to influence the properties of cell membranes, particularly in relation to various stresses, but biosynthesis of stigmasterol is poorly understood. Recently, however, Morikawa et al. (Plant Cell 18:1008-1022, 2006) showed in Arabidopsis thaliana that synthesis of stigmasterol and brassicasterol is catalyzed by two separate sterol C-22 desaturases, encoded by the genes CYP710A1 and CYP710A2, respectively. The proteins belong to a small cytochrome P450 subfamily having four members, denoted by CYP710A1-A4, and are related to the yeast sterol C-22 desaturase Erg5p acting in ergosterol synthesis. Here, we report on our parallel investigation of the Arabidopsis CYP710A family. To elucidate the function of CYP710A proteins, transgenic Arabidopsis plants were generated overexpressing CYP710A1 and CYP710A4. Compared to wild-type plants, both types of transformant displayed a normal phenotype, but contained increased levels of free stigmasterol and a concomitant decrease in the level of free sitosterol. CYP710A1 transformants also displayed higher levels of esterified forms of stigmasterol, cholesterol, 24-methylcholesterol and isofucosterol. The results confirm the findings of Morikawa et al. (Plant Cell 18:1008-1022, 2006) regarding the function of CYP710A1 in stigmasterol synthesis, and show that CYP710A4 also has this capacity. Furthermore, our results suggest that an increased stigmasterol level alone is sufficient to stimulate esterification of other major sterols.

Differential Effect of Plant Lipids on Membrane Organization

“…In agreement, using sterol biosynthesis mutants, a higher level of stigmasterol within plant PM has been correlated with altered fluidity and permeability characteristics (e.g. a restricted solute efflux) (98,99). Furthermore, the relative increase of more planar sterols, such as campesterol, reduced the membrane permeability to charged ions (87,100) and might favor ion exclusion.…”

Phytosterols Play a Key Role in Plant Innate Immunity against Bacterial Pathogens by Regulating Nutrient Efflux into the Apoplast

“…High levels of AtCYP710A1 gene transcripts were confirmed by qRT-PCR in Arabidopsis AtCYP710A1 gene overexpression lines ( Fig. 6A; Morikawa et al, 2006;Arnqvist et al, 2008). We challenged these plants through dip inoculation of host pathogen Psm (1 3 10 8 cfu/mL).…”

AtCYP710A1gene-mediated stigmasterol production plays a role in imparting temperature stress tolerance inArabidopsis thaliana

“…8 Sitosterol and stigmasterol are two major sterols present in Arabidopsis. 9,10 Higher levels of stigmasterol incorporation into the plasma membrane can alter the fluidity and permeability characteristics and restrict leakage of solutes from cytoplasm into the apoplastic region. 8,11 Further, sitosterol to stigmasterol ratio in the membrane has been known to influence the response of a cell to various biotic and abiotic stresses.…”