Pollen lipids are essential for sexual reproduction but our current knowledge regarding lipid dynamics in growing pollen tubes is still very scarce. Here, we report unique lipid composition and associated gene expression patterns during olive pollen germination. Up to 376 genes involved in the biosynthesis of all lipid classes, except suberin, cutin and lipopolysaccharides, are expressed in the olive pollen. The fatty acid profile of the olive pollen is markedly different compared with other plant organs. Triacylglycerol, containing mostly C12-C16 saturated fatty acids, constitutes the bulk of olive pollen lipids. These compounds are partially mobilized, and the released fatty acids enter the β-oxidation pathway to yield acetyl-CoA, which is converted into sugars through the glyoxylate cycle in the course of pollen germination. Our data suggest that fatty acids are synthesized de novo and incorporated into glycerolipids by the "eukaryotic pathway" in elongating pollen tubes. Phosphatidic acid is synthesized de novo in the endomembrane system during pollen germination and seems to have a central role in the pollen tube lipid metabolism. The coordinated action of fatty acid desaturases FAD2-3 and FAD3B might explain the increase of linoleic and alpha-linolenic acids observed in the germinating pollen. A continuous synthesis of triacylglycerol by the action of DGAT1 enzyme, but not PDAT, seems also plausible. All these data allow for a better understanding of the lipid metabolism during the olive reproduction process, which can impact in the future in the increase of olive fruit yield and, therefore, olive oil production.

中文翻译：

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橄榄（Olea europaea L.）花粉萌发和花粉管生长过程中的脂质组成和相关基因表达模式。

花粉脂质对于有性生殖是必不可少的，但是我们目前对生长中的花粉管中脂质动力学的了解仍然非常匮乏。在这里，我们报告橄榄花粉萌发过程中独特的脂质成分和相关的基因表达模式。橄榄花粉中表达了多达376个参与除脂蛋白，角质和脂多糖以外的所有脂质类别的生物合成的基因。橄榄花粉的脂肪酸谱与其他植物器官相比明显不同。三酰基甘油主要包含C12-C16饱和脂肪酸，构成了大部分的橄榄花粉脂质。这些化合物被部分动员，释放的脂肪酸进入β-氧化途径产生乙酰辅酶A，在花粉萌发过程中通过乙醛酸循环将其转化为糖。我们的数据表明，脂肪酸是从头合成的，并通过延长花粉管中的“真核途径”掺入甘油脂中。磷脂酸是在花粉萌发过程中在膜内系统中从头合成的，似乎在花粉管脂质代谢中具有重要作用。脂肪酸去饱和酶FAD2-3和FAD3B的协同作用可能解释了在发芽花粉中观察到的亚油酸和α-亚麻酸的增加。通过DGAT1酶而不是PDAT的作用连续合成三酰基甘油似乎也是可行的。所有这些数据使人们可以更好地了解橄榄繁殖过程中的脂质代谢，这可能会在将来影响橄榄果产量的增加，进而影响橄榄油的产量。