亚麻荠小RNA调控a-亚麻酸和种子大小

尽管小RNA在植物发育中的作用已经很明确，但它们在种子中的作用了解的较少，特别是对脂质代谢的影响，人们更是很少提及。近日，Chaofu Lu课题组发表在Plant Journal上题目为“Enhancing microRNA167A expression in seed decreases the a-linolenic acid content and increases seed size in Camelina sativa”的文章在这方面取得进展。在这项研究中，作者发现在种子特异性启动子的作用下，亚麻荠中microRNA167a（miR167oE）的过度表达改变了脂肪酸的组成，增加了种子的大小。具体来说，MIR167oE种子的a-亚麻酸含量较低，同时亚油酸含量也高于野生型。脂肪酸去饱和水平的降低对应于亚麻荠脂肪酸dsesaturase3（CSFAD3）在种子发育过程中的转录表达降低。MIR167能够靶向作用转录因子生长素响应因子（CSARF8），如之前在拟南芥中报道的那样。染色质免疫沉淀实验结合转录组分析表明，CSARF8与bZIP67和ABI3基因启动子结合。这些转录因子直接或者通过ABI3-bZIP12途径调节CSFAD3的表达并影响α-亚麻酸的积累。除了揭示MIR167A-CSARF8介导的抑制CSFAD3的转录外，作者还进行了转录组分析，以揭示调控亚麻荠种子大小的机制。许多基因的表达水平在MIR167oE中发生了改变，包括以前被鉴定为影响其他植物种子大小的基因。最显著的是，种皮发育的基因，如亚精和木质素的生物合成被下调。本研究对亚麻荠脂肪酸代谢和种子大小测定的调控机制提供了有价值的见解，并提出了改善这些重要性状的可能途径。

Summary

Despite well-established roles of microRNAs in plant development, little has been addressed to understand their effects in seeds especially on lipid metabolism. In this study, we showed that overexpressing microRNA167A (miR167OE) in camelina (Camelina sativa) under a seed-specific promoter changed fatty acid composition and increased seed size. Specifically, the miR167OE seeds had a lower a-linolenic acid with a concomitantly higher linoleic acid content than the wild type. This decreased level of fatty acid desaturation corresponded to a decreased transcriptional expression of the camelina fatty acid dsesaturase3 (CsFAD3) in developing seeds. MiR167 targeted the transcription factor auxin response factor (CsARF8) in camelina, as had been reported previously in Arabidopsis. Chromatin immunoprecipitation experiments combined with transcriptome analysis indicated that CsARF8 bound to promoters of camelina bZIP67 and ABI3 genes. These transcription factors directly or through the ABI3-bZIP12 pathway regulate CsFAD3 expression and affect the a-linolenic acid accumulation. In addition to decipher the miR167A-CsARF8 mediated transcriptional cascade for CsFAD3 suppression, transcriptome analysis was conducted to implicate mechanisms that regulate seed size in camelina. Expression levels of many genes were altered in miR167OE, including orthologs that have previously been identified to affect seed size in other plants. Most notably, genes for seed coat development such as suberin and lignin biosynthesis were down-regulated. This study provides valuable insights on regulatory mechanism of fatty acid metabolism and seed size determination, and suggests possible approaches to improve these important traits in camelina.

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