PvNAC1 and PvNAC2 Are Associated with Leaf Senescence and Nitrogen Use Efficiency in Switchgrass
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Two full-length cDNAs encoding NAM, ATAF, and CUC (NAC)-family transcription factors (TFs) were isolated from two different cultivars of Panicum virgatum L. (switchgrass) and named PvNAC1 and PvNAC2. Phylogenetic analysis of PvNAC1 and PvNAC2 grouped them with NAC proteins involved in senescence in annual plant species. Transcript profiling revealed that both PvNAC1 and PvNAC2 are induced during leaf senescence. Expression of a PvNAC1-green fluorescent protein (GFP) fusion in plant cells revealed a nuclear location of the protein, consistent with a role in transcriptional regulation. Expression of PvNAC1 in an Arabidopsis nap stay-green mutant suppressed its senescence defect. Expression of PvNAC1 in wild-type Arabidopsis triggered early leaf senescence and remobilization. Transcriptome analysis implicated leaf protein degradation and nitrogen recycling enzymes in NAC-dependent seed protein increase in Arabidopsis. Overexpression of pvNAC2 in switchgrass resulted in increased aboveground biomass associated with increased transcript levels of key nitrogen metabolism genes in leaves and nitrate and ammonium transporter genes in roots. The results indicate that NAC TFs play conserved roles in leaf senescence in the plant kingdom not only in annual monocots and dicots but also in perennial plants such as switchgrass. PvNAC1 and PvNAC2 hold promise for improving nutrient use efficiency in switchgrass through genetic manipulation.
KeywordsSwitchgrass NAC Senescence Nitrogen remobilization/uptake
We thank Prof. Arvid Boe (Plant Science Department, South Dakota State University) for generously providing seeds of switchgrass cultivar Summer and Dr. Albrecht von Arnim (Department of BCMB, University of Tennessee) for the gift pAVA121 vector. We also thank Jianfei Yun for the help with collecting switchgrass samples and caring for Arabidopsis plants. This work was supported by the Office of Biological and Environmental Research of the US Department of Energy via the BioEnergy Science Center (BESC) (grant number DE-PS02-06ER64304) and by the Samuel Roberts Noble Foundation.
Conflict of Interest
The authors have no conflict of interest to declare.
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