The Sequential Action of miR156 and miR172 Regulates Developmental Timing in Arabidopsis

Abstract

SUMMARY The transition from the juvenile to the adult phase of shoot development in plants is accompanied by changes in vegetative morphology and an increase in reproductive potential. Here we describe the regulatory mechanism of this transition. We show that miR156 is necessary and sufficient for the expression of the juvenile phase, and regulates the timing of the juvenile-to-adult transition by coordinating the expression of several pathways that control different aspects of this process. miR156 acts by repressing the expression of functionally distinct SPL transcription factors. miR172 acts downstream of miR156 to promote adult epidermal identity. miR156 regulates the expression of miR172 via SPL9 which, redundantly with SPL10, directly promotes the transcription of miR172b. Thus, like the larval-to-adult transition in Caenorhabditis elegans, the juvenile-to-adult transition in Arabidopsis is mediated by sequentially operating miRNAs. miR156 and miR172 are positively regulated by the transcription factors they target, suggesting that negative feedback loops contribute to the stability of the juvenile and adult phases.

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“…4) (refs 29,31). SPL9, À 10, À 2, À 3, À 11, À 13 and À 15 have been shown to function similarly and redundantly with each other in regulation of the juvenile-to-adult phase transition and flowering time [29][30][31][32][33][34][35][36] . SPLs also feedback-regulate miR156 precursor transcription 29 .…”

“…Specifically, miR156 is known to target and suppress the expressions of 10 SPL transcription factors, including SPL2, À 3, À 4, À 5, À 6, À 9, À 10, À 11, À 13 and À 15 (ref. 29). MiR157 shares 85.7% sequence identity with miR156, and both miRNAs suppress SPLs similarly 30 .…”

“…4a). It is well-established that the sequential action of the components in this pathway controls the vegetative juvenile-to-adult phase transition and flowering time during normal development 29 . Specifically, miR156 is known to target and suppress the expressions of 10 SPL transcription factors, including SPL2, À 3, À 4, À 5, À 6, À 9, À 10, À 11, À 13 and À 15 (ref.…”

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“…SPL2 and MFB16.6 are involved in vegetative and reproduction phases and regulate the floral transitions [78]. miR172B regulated by SPL10 [79] also, MiR172B was indirectly regulated by miR156/157 family members (Fig. 9).…”

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“…9 Similarly, miR156-SPLs, miR172-AP2 also form as 2 negative feedback loops in regulation of developmental timing in Arabidopsis. 10 Moreover, the miRNA-regulated TFs usually have multiple duplicates in the plant genome and preserve the same miRNA-binding sites. Therefore a single miRNAs usually regulate multiple closely related TFs, making it at the hub of miRNA-TF-genes networks (Fig.…”