Objective  NACs in petunia responsible for the growth, floral senescence, and stress response were identified and analyzed.

  Method  Based on the Petunia axillaris genome, transcriptomes on the flower in senescence as well as some other organs under the stress of inoculated tobacco rattle virus (TRV), low phosphorus, low temperature, NaCl, copper ion, or drought were obtained. Expression under stress, cis-acting elements, and transcription factor binding sites in promoters of differentially expressed PaNACs were analyzed. The expression in flower senescence was determined using qRT-PCR, and putative target genes of proteins encoded by them predicted.

  Result  Of the 131 PaNACs, 59 (i.e., 45.04% of all) were identified as differentially expressed genes (DEGs) during flower senescence and in response to stresses. PaNAC72, PaNAC22, PaNAC29, PaNAC40, PaNAC2, PaNAC90, PaNAC83, PaNAC56, PaNAC36, and PaNAC35 exhibited significant differential expressions in response to at least 3 stress treatments. Among them, PaNAC29, an orthologue of the Arabidopsis key senescence-related gene AtNAP, was highly upregulated during flower senescence and in response to low temperature, low phosphorus, or copper ion treatment. PaNAC72 was significantly affected by all except copper ion treatment. PaNAC22 was upregulated during flower senescence and in responses to low temperature and low phosphorus treatments but downregulated in the presence of copper ion or under drought condition. Multiple stress responsive elements presented in the promoters of the 10 PaNACs, and many senescence and stress responsive DEGs containing NAC binding sites in their promoters.

  Conclusion  NAC (NAM, ATAF and CUC) involved widely in the growth, development, and stress responses of plants. PaNACs in petunia, such as PaNAC29 appeared to be a key positive regulator of floral senescence, and PaNAC72 responsive to a wide variety of stresses.