The role of the integuments in pollen tube guidance in flowering plants

First author: Jorge Lora; Affiliations: Instituto de Hortofruticultura Subtropical y Mediterránea ‘La Mayora’ IHSM‐UMA‐CSIC: Málaga, Spain

Corresponding author: Jorge Lora

In angiosperms, pollen tube entry into the ovule generally takes place through the micropyle (珠孔), but the exact role of the micropyle in pollen tube guidance remains unclear. A limited number of studies have examined eudicots with bitegmic micropyles (双珠被珠孔), but information is lacking in ovules of basal/early‐divergent angiosperms with unitegmic micropyles (单珠被珠孔). We have evaluated the role of the micropyle in pollen tube guidance in an early‐divergent angiosperm (Annona cherimola; 毛叶番荔枝) and the evolutionarily derived Arabidopsis thaliana by studying γ‐aminobutyric acid (GABA; γ-氨基丁酸) and arabinogalactan proteins (AGPs; 阿拉伯半乳聚糖蛋白) in wild‐ ype plants and integument‐defective mutants. A conserved inhibitory role of GABA in pollen tube growth was shown in A. cherimola, in which AGPs surround the egg apparatus (卵器). In Arabidopsis, the micropyle formed only by the outer integument in wuschel‐7 mutants caused a partial defect in pollen tube guidance. Moreover, pollen tubes were not observed in the micropyle of an inner no outer (ino) mutant in Arabidopsis, but were observed in homologous ino mutants in Annona. The similar distribution of GABA and AGPs observed in the micropyle of Arabidopsis and Annona, together with the anomalies (异常) from specific integument mutants, support the role of the inner integument in preventing multiple tube entrance (polytubey; 多个花粉管进入) in these two phylogenetically distant genera.

在被子植物中，花粉管通常是通过珠孔进入到胚珠当中，但珠孔在花粉管导向中的作用还不清楚。已经有一些报道研究了具有双珠被珠孔的双子叶植物，但对于具有单珠被珠孔的早期分化的被子植物还所知甚少。本文通过研究γ-氨基丁酸GABA和阿拉伯半乳聚糖蛋白AGP在野生型和珠被缺陷突变体中的功能，研究早期分化被子植物毛叶番荔枝及演化上同起源的拟南芥中珠孔在花粉管导向中的作用。毛叶番荔枝具有保守的GABA抑制花粉管生长功能，而AGP围绕在卵器周边。在拟南芥wuschel‐7突变体中，珠孔仅在外珠被中形成，导致了花粉管导向的部分缺陷。此外，在拟南芥ino突变体的珠孔中并未观察到花粉管，但在毛叶番荔枝同源ino突变体中却观察到了花粉管。在拟南芥和毛叶番荔枝珠孔中类似的GABA和AGP分布，以及特定珠被缺陷突变体的异常说明了在这两个不同的物种中，内珠被都在防止胚珠与多个花粉管结合中发挥重要作用。

doi: https://doi.org/10.1111/nph.15420

Journal: New Phytologist

First Published: 31 August, 2018

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