A cyanobacterial gene, sqdX, required for biosynthesis of the sulfolipid sulfoquinovosyldiacylglycerol

Abstract

The sulfolipid sulfoquinovosyldiacylglycerol is present in the photosynthetic membranes of plants and many photosynthetic bacteria. A novel gene, sqdX, essential for sulfolipid biosynthesis in the cyanobacterium Synechococcus sp. strain PCC7942 is proposed to encode the cyanobacterial sulfolipid synthase catalyzing the last reaction of the pathway.

FIG. 1

Insertional inactivation of sqdX. (A) Restriction and ORF map of the plasmid pSYB and the inactivation plasmid pDL2. The black bar indicates the location of the probe used for hybridization, and the open arrow indicates the neomycin phosphotransferase cassette. Restriction sites: A, BamHI; E, SpeI; H, HindIII; K, KpnI; O, XhoI; P, PstI; S, SalI. (B) Autoradiograph of a Southern blot showing genomic DNA from Synechococcus wild type and 7942ΔsqdX mutant. The DNA was cleaved with HindIII and probed with the fragment indicated in A. The approximate size of the three diagnostic fragments is indicated in kb.

FIG. 2

Separation of ³⁵S-labeled lipids from Synechococcus wild type and 7942ΔsqdX mutant (ΔX). Either equal amounts of undiluted lipids (undil.) or serial dilutions of the wild-type extract, as indicated, were spotted. The sulfolipid band is marked SQDG. Compounds were visualized by autoradiography.

FIG. 3

Genetic complementation of the Synechococcus 7942ΔsqdX mutant. Lipid extracts from Synechococcus wild type (WT) and mutant strain 7942ΔsqdX carrying plasmids as indicated were separated by thin-layer chromatography. Lipids were visualized by exposure to iodine vapor. DGDG, diagalactosyldiacylglycerol; MGDG, monogalactosyldiacylglycerol; PG, phosphatidylglycerol; SQDG, sulfoquinovosyldiacylglycerol