Loss of THIN EXINE2 disrupts multiple processes in the mechanism of pollen exine formation.
Loss of THIN EXINE2 disrupts multiple processes in the mechanism of pollen exine formation.
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DOI：
10.1093/plphys/kiab244
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发表时间：
2021-05
期刊：
影响因子：
7.4
通讯作者：
Rui Wang;A. Dobritsa
中科院分区：
文献类型：
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作者：
Rui Wang;A. Dobritsa
外壁，花粉壁的基于孢粉素的外层，通过一种不同寻常的机制形成，涉及两种花药细胞类型：发育中的花粉和绒毡层。孢粉素前体和其他组成外壁所需的成分是如何从绒毡层传递到花粉中并在花粉表面聚集的，目前还不清楚。在这里，我们描述了一个拟南芥（Arabidopsis thaliana）突变体，thin exine2 (tex2)，它产生的花粉具有异常薄的外壁。TEX2基因（也被称为细胞分裂素缺陷抑制因子1 (ROCK1)）编码一种定位于内质网的核苷酸-糖转运蛋白。毡层表达TEX2足以保证正常的外阴发育。TEX2的缺失导致异常原胺的形成，缺乏初级外壁元件，以及随后孢子花粉素无法正确组装成外壁结构。利用免疫组织化学，我们研究了tex2 primesine的碳水化合物组成，发现它积累了更多的阿拉伯半乳聚糖。tex2绒毡层积累了显著的代谢包涵体，这些包涵体依赖于孢粉聚酮的生物合成和运输，可能与孢粉蛋白样物质相对应。尽管之前没有报道过这样的内含物，但我们发现，已知的孢粉素生物合成基因之一LAP5/PKSB的突变，而其平行基因LAP6/PKSA的突变，也会导致类似内含物的积累，这表明这两个类似基因的作用是不同的。最后，我们发现tex2绒毡层内含物以及tex2和其他外显子基因双突变体的合成致死性可以作为研究参与外显子形成的基因之间遗传关系的报告基因。
Exine, the sporopollenin-based outer layer of the pollen wall, forms through an unusual mechanism involving interactions between two anther cell types: developing pollen and tapetum. How sporopollenin precursors and other components required for exine formation are delivered from tapetum to pollen and assemble on the pollen surface is still largely unclear. Here, we characterized an Arabidopsis (Arabidopsis thaliana) mutant, thin exine2 (tex2), which develops pollen with abnormally thin exine. The TEX2 gene (also known as REPRESSOR OF CYTOKININ DEFICIENCY1 (ROCK1)) encodes a putative nucleotide-sugar transporter localized to the endoplasmic reticulum. Tapetal expression of TEX2 is sufficient for proper exine development. Loss of TEX2 leads to the formation of abnormal primexine, lack of primary exine elements, and subsequent failure of sporopollenin to correctly assemble into exine structures. Using immunohistochemistry, we investigated the carbohydrate composition of the tex2 primexine and found it accumulates increased amounts of arabinogalactans. Tapetum in tex2 accumulates prominent metabolic inclusions which depend on the sporopollenin polyketide biosynthesis and transport and likely correspond to a sporopollenin-like material. Even though such inclusions have not been previously reported, we show mutations in one of the known sporopollenin biosynthesis genes, LAP5/PKSB, but not in its paralog LAP6/PKSA, also lead to accumulation of similar inclusions, suggesting separate roles for the two paralogs. Finally, we show tex2 tapetal inclusions, as well as synthetic lethality in the double mutants of TEX2 and other exine genes, could be used as reporters when investigating genetic relationships between genes involved in exine formation.