Abstract
CmNACP1 mRNA has been shown to move long distance through the phloem in Cucurbita maxima (pumpkin) and through a graft junction. Whereas the phloem transport of several different mRNAs has been documented in other systems as well, its function remains, for most of these RNAs, largely unknown. To gain insight into the possible role of these RNAs, we searched for the closest homologs of CmNACP1 in Arabidopsis, a model plant much more amenable for analysis. A phylogenetic approach using the predicted NAC domain indicated that ANAC059, ANAC092, ANAC079, ANAC100, ANAC046, and ANAC087 form a single clade with CmNACP1. In the present work, we analyzed the possible function of the ANAC087 gene in more detail. The promoter region of this gene directed expression in the vasculature, and also in trichomes, stem, apexes, and developing flowers which supports the notion that ANAC087 and CmNACP1 are orthologs. Overexpression of the ANAC087 gene induced increased branching in inflorescence stem, and also development of ectopic or aerial rosettes in T1 and T2 plants. Furthermore, overexpression of ANAC087 leads to accelerated leaf senescence in 44 days post-germination (dpg). Interestingly, a similar phenotype was observed in plants expressing the ANAC087 gene upstream region, also showing an increase in ANAC087 transcript levels. Finally, the results shown in this work indicate a role for ANAC087 in leaf senescence and also in rosette development.
Highlights
The NAC proteins (NACs) domain family of transcription factors is ubiquitous in plants playing diverse important roles in development and response to external stimuli
We found that CmNACP1 forms a clade with ANAC087 (At5g18270) and ANAC046 (At3g04060), among other NAC proteins related to induction of cell death and senescence
To identify the protein homologs for CmNACP1 in Arabidopsis, we performed a BLAST alignment with the CmNACP1 NAC domain reported in UniProt Knowledgebase, since the complete virtually translated sequences are of varying lengths, and sequences outside the NAC domain are highly divergent in members of the family, even within the same species
Summary
The NAC domain (for Petunia NAM, and Arabidopsis ATAF1, ATAF2 and CUC2) family of transcription factors is ubiquitous in plants playing diverse important roles in development and response to external stimuli. Certain NAC domain proteins have been shown to enhance senescence, in some cases through binding to conserved sequences in the upstream region of target genes, for example, those involved in the degradation of chlorophyll (Guo and Gan, 2006; Balazadeh et al, 2010; Kim et al, 2016) This protein family has been analyzed in detail mostly in Arabidopsis; less is known regarding their function in other species. Other NAC genes are negative regulators of leaf senescence, for example, ANAC042 (JUB1) and ANAC083 (VNI2) (Yang et al, 2011; Wu et al, 2012)
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