ABCG15 Encodes an ABC Transporter Protein, and is Essential for Post-Meiotic Anther and Pollen Exine Development in Rice

In flowering plants, anther and pollen development is critical for male reproductive success. The anther cuticle and pollen exine play an essential role, and in many cereals, such as rice, orbicules/ubisch bodies are also thought to be important for pollen development. The formation of the anther cuticle, exine and orbicules is associated with the biosynthesis and transport of wax, cutin and sporopollenin components. Recently, progress has been made in understanding the biosynthesis of sporopollenin and cutin components in Arabidopsis and rice, but less is known about the mechanisms by which they are transported to the sites of deposition. Here, we report that the rice ATP-binding cassette (ABC) transporter, ABCG15, is essential for postmeiotic anther and pollen development, and is proposed to play a role in the transport of rice anther cuticle and sporopollenin precursors. ABCG15 is highly expressed in the tapetum at the young microspore stage, and the abcg15 mutant exhibits small, white anthers lacking mature pollen, lipidic cuticle, orbicules and pollen exine. Gas chromatography-mass spectrometry (GC-MS) analysis of the abcg15 anther cuticle revealed significant reductions in a number of wax components and aliphatic cutin monomers. The expression level of genes involved in lipid metabolism in the abcg15 mutant was significantly different from their levels in the wild type, possibly due to perturbations in the homeostasis of anther lipid metabolism. Our study provides new insights for understanding the molecular mechanism of the formation of the anther cuticle, orbicules and pollen wall, as well as the machinery for lipid metabolism in rice anthers.