Piffanelli P, Ross J H, Murphy D J
Department of Brassica and Oilseeds Research, John Innes Centre, Norwich, UK.
Plant J. 1997 Mar;11(3):549-62. doi: 10.1046/j.1365-313x.1997.11030549.x.
Pollen development in angiosperms is regulated by the interaction of products contributed by both the gametophytic (haploid) and sporophytic (diploid) genomes. In entomophilous species, lipids are major products of both sporophytic and gametophytic metabolism during pollen development. Mature pollen grains of Brassica napus are shown to contain three major acyl lipid pools as follows: (i) the extracellular tryphine mainly consisting of medium-chain neutral esters; (ii) the intracellular membranes, particularly endoplasmic reticulum, mainly containing phospholipids; and (iii) the intracellular storage lipids, which are mostly triacylglycerols. This paper reports on the kinetics of accumulation of these lipid classes during pollen maturation and the expression patterns of several lipid biosynthetic genes and their protein products that are differentially regulated in developing microspores/ pollen grains (gametophyte) and tapetal cells (sporophyte) of B. napus. Detailed analysis of three members of the stearoyl-ACP desaturase (sad) gene family by Northern blotting, in situ hybridization and RT-PCR showed that the same individual genes were expressed both in gametophytic and sporophytic tissues, although under different temporal regulation. In the tapetum, maximal expression of two marker genes for lipid biosynthesis (sad and ear) occurred at a bud length of 2-3 mm, and the corresponding gene products SAD and EAR were detected by Western blotting in 3-4 mm buds, coinciding with the maximal rates of tapetal lipid accumulation. These lipids are released following tapetal cell disintegration and are relocated to form the major structural component of the extracellular tryphine layer that coats the mature pollen grain. In contrast, in developing microspores/pollen grains, maximal expression of the lipid marker genes sad, ear, acp and cyb5 was at the 3-5 mm bud stages, with the SAD and EAR gene products detected in 4-7 mm buds. This pattern of expression coincided with accumulation of the intracellular storage and membrane lipid components of pollen. These results suggest that, although the same genes may be expressed in the sporophytic tapetal cells and in gametophytic tissues, they are regulated differentially leading to the production of the various contrasting lipidic structures that are assembled together to give rise to a viable, fertile pollen grain.
被子植物花粉的发育受配子体（单倍体）和孢子体（二倍体）基因组产物相互作用的调控。在虫媒花物种中，脂质是花粉发育过程中孢子体和配子体代谢的主要产物。甘蓝型油菜的成熟花粉粒含有三种主要的酰基脂质库，如下所示：（i）细胞外的类脂体，主要由中链中性酯组成；（ii）细胞内膜，特别是内质网，主要含有磷脂；（iii）细胞内储存脂质，主要是三酰甘油。本文报道了这些脂质类在花粉成熟过程中的积累动力学，以及几个脂质生物合成基因及其蛋白质产物在甘蓝型油菜发育中的小孢子/花粉粒（配子体）和绒毡层细胞（孢子体）中差异调控的表达模式。通过Northern印迹、原位杂交和RT-PCR对硬脂酰-ACP去饱和酶（sad）基因家族的三个成员进行详细分析表明，相同的单个基因在配子体和孢子体组织中均有表达，尽管其受到不同的时间调控。在绒毡层中，脂质生物合成的两个标记基因（sad和ear）在花蕾长度为2-3毫米时表达量最高，通过蛋白质免疫印迹法在3-4毫米的花蕾中检测到相应的基因产物SAD和EAR，这与绒毡层脂质积累的最大速率一致。这些脂质在绒毡层细胞解体后释放出来，并重新定位形成覆盖成熟花粉粒的细胞外类脂体层的主要结构成分。相反，在发育中的小孢子/花粉粒中，脂质标记基因sad、ear、acp和cyb5在花蕾3-5毫米阶段表达量最高，在4-7毫米的花蕾中检测到SAD和EAR基因产物。这种表达模式与花粉细胞内储存脂质和膜脂成分的积累一致。这些结果表明，尽管相同的基因可能在孢子体绒毡层细胞和配子体组织中表达，但它们受到差异调控，导致产生各种不同的脂质结构，这些结构组装在一起形成一个有活力、可育的花粉粒。
