EMBO:拟南芥 EXPORTIN5同源基因 HASTY 调节细胞间和维管束间的 microRNA 运动

植物microRNAs（microRNAs）引导产生细胞内以及远处细胞和组织中序列互补转录物的胞浆转录后基因沉默。在这里，我们利用拟南芥中一个基于miRNA的人工系统（amiRSUL），通过正向遗传学来探索细胞间miRNA运动的机制。该筛选鉴定了许多突变的等位基因HASTY（HST），这是哺乳动物EXPORTIN5（XPO5）的直系同源基因，在拟南芥的miRNA生物发生中起作用。在表皮剥离和移植实验中，miRNA受体组织的amiRSUL水平比沉默发射组织的显著降低。我们将这种效应归因于HST除了调节其生物发生外，还控制细胞间和韧皮部介导的加工无芒刺的运动。虽然HST不是游离GFP或siRNAs运动所必需的，但其在amiRSUL组织中的细胞自主表达足以恢复amiRSUL运动，而不依赖于其核-胞质穿梭活动。相比之下，HST对受体组织内amiRSUL 的运动和活性是不必要的。最后，HST使内源性miRNAs在HST突变组织中的稳态水平基本保持不变。我们讨论了HST作为迄今为止未被认识的miRNA运动调节器的作用，它与最近在miRNA转录和miRNA加工的关系中分配的核功能有关。

amiRSUL 通过筛分子在细胞间和长距离移动

植物microRNAs（miRNAs）的通过维管细胞间和远距离移动，但其潜在机制仍不清楚。在这里，拟南芥Exportin 5（XPO5）同系物HASTY（HST）被发现以一种可能与microRNA发射细胞核内microRNA生物发生结合的方式调节这两种类型的运动。

Plant microRNAs (miRNAs) guide cytosolic post-transcriptional gene silencing of sequence-complementary transcripts within the producing cells, as well as in distant cells and tissues. Here, we used an artificial miRNA-based system (amiRSUL) in Arabidopsis thaliana to explore the still elusive mechanisms of inter-cellular miRNA movement via forward genetics. This screen identified many mutant alleles of HASTY (HST), the ortholog of mammalian EXPORTIN5 (XPO5) with a recently reported role in miRNA biogenesis in Arabidopsis. In both epidermis-peeling and grafting assays, amiRSUL levels were reduced much more substantially in miRNA-recipient tissues than in silencing-emitting tissues. We ascribe this effect to HST controlling cell-to-cell and phloem-mediated movement of the processed amiRSUL, in addition to regulating its biogenesis. While HST is not required for the movement of free GFP or siRNAs, its cell-autonomous expression in amiRSUL-emitting tissues suffices to restore amiRSUL movement independently of its nucleo-cytosolic shuttling activity. By contrast, HST is dispensable for the movement and activity of amiRSUL within recipient tissues. Finally, HST enables movement of endogenous miRNAs that display mostly unaltered steady-state levels in hst mutant tissues. We discuss a role for HST as a hitherto unrecognized regulator of miRNA movement in relation to its recently assigned nuclear function at the nexus of MIRNA transcription and miRNA processing.

https://www.embopress.org/doi/full/10.15252/embj.2020107455?af=R

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