miRNAs (microRNAs) are ~ 21-nt non-coding small RNAs (sRNAs) that play crucial regulatory roles in plant biotic and abiotic stress responses. Phosphorus (Pi) deficiency constrains plant growth and reduces yields worldwide. To identify tree miRNAs and evaluate their functions in the response to low Pi, we identified 261 known and 31 candidate novel miRNA families from three sRNA libraries constructed from Populus tomentosa subjected to sufficient or Pi deficiency condition or to restoration of a sufficient Pi level after Pi deficiency. Pi deficiency resulted in significant changes in the abundance of TPM (transcript per million) of 65 known and 3 novel miRNAs. Interestingly, four miRNAs responsive to low N—miR167, miR394, miR171, and miR857—were found to be involved in the response to low Pi. Thirty-five known and one novel miRNAs responded dynamically to Pi fluctuations, suggesting their involvement in the response to Pi deficiency. miRNA clusters comprising 36 miRNAs were identified in 10 chromosomes. Intriguingly, nine pairs of sense and antisense miRNAs transcribed from the same loci were detected in P. tomentosa, which is the first such report in woody plants. Moreover, target genes of the known miRNAs and novel miRNA candidates with significantly changed abundance were predicted, and their functions were annotated. Degradome sequencing supported the identified targets of miRNAs in P. tomentosa. These findings will enhance our understanding of universal and specific molecular regulatory mechanisms of trees under nutrition stress and may facilitate improvement of the Pi utilization efficiency of woody plants.

中文翻译：

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全转录组鉴定和表征毛白杨中磷酸盐饥饿的microRNA。

miRNA（microRNA）是〜21 nt的非编码小RNA（sRNA），在植物生物和非生物胁迫响应中起着至关重要的调节作用。磷（Pi）缺乏限制了植物的生长并降低了全球产量。为了鉴定树中的miRNA并评估其在低磷响应中的功能，我们从毛白杨构建的三个sRNA文库中鉴定出261个已知的miRNA家族和31个候选新miRNA家族。在Pi缺乏后遭受充分或Pi缺乏的状况或恢复足够的Pi水平。Pi缺乏导致65种已知miRNA和3种新颖miRNA的TPM丰度（每百万转录本）发生显着变化。有趣的是，发现对低N反应的四个miRNA – miR167，miR394，miR171和miR857 –参与了对低Pi的反应。35种已知的miRNA和一种新颖的miRNA对Pi波动动态响应，表明它们参与了对Pi缺乏的响应。在10条染色体中鉴定出包含36个miRNA的miRNA簇。有趣的是，在毛绒球菌中检测到从同一基因座转录的九对有义和反义miRNA 。，这是木本植物中的第一个此类报告。此外，预测了已知miRNA的靶基因和丰度发生显着变化的新型miRNA候选物，并对其功能进行了注释。降解组测序支持miRNA的确定的目标在毛白杨。这些发现将增进我们对营养压力下树木的通用和特定分子调控机制的理解，并可能有助于提高木本植物的Pi利用率。