The mevalonate pathway but not the methylerythritol phosphate pathway is critical for elaioplast and pollen coat development in Arabidopsis

Pollen coat components are derived from tapetum cells, which contain elaioplasts derived from plastids and tapetosome derived from the endoplasmic reticulum. In Brassica napus, the main neutral lipids in the elaioplast and tapetosome have been reported to be sterol ester and triacylglycerol, respectively. Isopentenyl pyrophosphate, the structural component of sterol, is produced via the cytosolic mevalonate (MVA) and plastidic methylerythritol phosphate (MEP) pathways. Although these two pathways are compartmentalized, partial cross-talk between them has been reported. To investigate the contribution of these two pathways in elaioplast formation, we characterized mutant pollen of these two pathways. We observed the anthers of male sterile hmg1-1 and atipi1 atipi2 mutants ultrastructurally, which were deficient in MVA pathway enzymes. hmg1-1 and atipi1atipi2 showed a shrunken elaioplast inner granule at the bicellular pollen stage. Conversely, in the cla1-1 mutant, which showed a defective MEP pathway, elaioplast development was normal. The pollen of hmg1-1 and atipi1atipi2 was coatless, whereas cla1-1 had a pollen coat. These results indicate that the MVA pathway but not the MEP pathway is critical for elaioplast development though the organelle is derived from plastids.