title: Regulatory network of microRNA399 and PHO2 by systemic signaling.
abstract: Recently, we showed that microRNA399s (miR399s) control inorganic phosphate (Pi) homeostasis by regulating the expression of PHO2 encoding a ubiquitin-conjugating E2 enzyme 24. Arabidopsis (Arabidopsis thaliana) plants overexpressing miR399 or the pho2 mutant overaccumulate Pi in shoots. The association of Pi translocation and coexpression of miR399s and PHO2 in vascular tissues suggests their involvement in long-distance signaling. In this study, we used reciprocal grafting between wild-type and miR399-overexpressing transgenic plants to dissect the systemic roles of miR399 and PHO2. Arabidopsis rootstocks overexpressing miR399 showed high accumulation of Pi in the wild-type scions because of reduced PHO2 expression in the rootstocks. Although miR399 precursors or expression was not detected, we found a small but substantial amount of mature miR399 in the wild-type rootstocks grafted with transgenic scions, which indicates the movement of miR399 from shoots to roots. Suppression of PHO2 with miR399b or c was less efficient than that with miR399f. Of note, findings in grafted Arabidopsis were also discovered in grafted tobacco (Nicotiana benthamiana) plants. The analysis of the pho1 mutant provides additional support for systemic suppression of PHO2 by the movement of miR399 from Pi-depleted shoots to Pi-sufficient roots. We propose that the long-distance movement of miR399s from shoots to roots is crucial to enhance Pi uptake and translocation during the onset of Pi deficiency. Moreover, PHO2 small interfering RNAs mediated by the cleavage of miR399s may function to refine the suppression of PHO2. The regulation of miR399 and PHO2 via long-distance communication in response to Pi deficiency is discussed.
authors.affiliation: Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan, Republic of China.
authors.forename: Shu-I
authors.initials: SI
authors.lastname: Lin
authors.forename: Su-Fen
authors.initials: SF
authors.lastname: Chiang
authors.forename: Wei-Yi
authors.initials: WY
authors.lastname: Lin
authors.forename: June-Wei
authors.initials: JW
authors.lastname: Chen
authors.forename: Ching-Ying
authors.initials: CY
authors.lastname: Tseng
authors.forename: Pei-Chi
authors.initials: PC
authors.lastname: Wu
authors.forename: Tzyy-Jen
authors.initials: TJ
authors.lastname: Chiou
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics*; D001483:Base Sequence; D035683:MicroRNAs / Q000235:genetics*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction; D014026:Nicotiana / Q000235:genetics; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; D035683:MicroRNAs; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C514696:UBC24 protein, Arabidopsis; D044763:Ubiquitin-Conjugating Enzymes