Abstract
Auxin response factors (ARFs) are important regulators modulating the expression of auxin-responsive genes in various biological processes in plants. In the Populus genome, a total of 39 ARF members have been identified, but their detailed functions are still unclear. In this study, six poplar auxin response factor 2 (PtrARF2) members were isolated from P. trichocarpa. Expression pattern analysis showed that PtrARF2.1 is highly expressed in leaf tissues compared with other PtrARF2 genes and significantly repressed by exogenous auxin treatment. PtrARF2.1 is a nuclear-localized protein without transcriptional activation activity. Knockdown of PtrARF2.1 by RNA interference (RNAi) in poplars led to the dwarf plant, altered leaf shape, and reduced size of the leaf blade, while overexpression of PtrARF2.1 resulted in a slight reduction in plant height and the similar leaf phenotype in contrast to the wildtype. Furthermore, histological staining analysis revealed an ectopic deposition of lignin in leaf veins and petioles of PtrARF2.1-RNAi lines. RNA-Seq analysis showed that 74 differential expression genes (DEGs) belonging to 12 transcription factor families, such as NAM, ATAF and CUC (NAC), v-myb avian myeloblastosis viral oncogene homolog (MYB), ethylene response factors (ERF) and basic helix–loop–helix (bHLH), were identified in PtrARF2.1-RNAi leaves and other 24 DEGs were associated with the lignin biosynthetic pathway. Altogether, the data indicate that PtrARF2.1 plays an important role in regulating leaf development and influences the lignin biosynthesis in poplars.
Highlights
IntroductionLeaf development is a dynamic and complex process thatrespondsto internal and external cues
In higher plants, leaf development is a dynamic and complex process thatrespondsto internal and external cues
It has been revealed that AtARF2 factor is a pleiotropic developmental regulator and modulates the leaf development and senescence [21,36]
Summary
Leaf development is a dynamic and complex process thatrespondsto internal and external cues. A simple leaf has a single, continuous lamina, whereas a compound leaf contains multiple subunits termed leaflets, each resembling a simple leaf [1] Several phytohormones, such as auxin (IAA), cytokinins (CK), gibberellins (GA) and jasmonic acid (JA), are involved in the leaf initiation and development [2]. Leaves are derived from small populations of founder cells set aside on the flanks of the pluripotent shoot apical meristem (SAM), and auxin acts as a central regulator of this process. These are generated by auxin biosynthesis in the SAM and by directional auxin transport facilitated by the PIN-FORMED1 (PIN1) auxin transporter [6,7]. Mutation of three auxin importers (aux1/lax1/lax2) is required for delaying the serration growth [11]
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