Transcriptome-Wide Identification and Response Pattern Analysis of the NAC Transcription Factor in Response to Pb Stress.

The NAC (NAM-ATAF1/2-CUC) transcription factor family is one of the largest plant-specific transcription factor families, playing an important role in plant growth and development and abiotic stress response. As a short-rotation woody plant, () has high lead (Pb) phytoremediation potential. To understand the role of NAC in Pb tolerance, 53 transcripts were identified using third-generation and next-generation transcriptomic data from exposed to Pb stress, and a phylogenetic analysis revealed 11 subfamilies. A sequence alignment showed that multiple subfamilies represented by TIP and ATAF had a gene that produced more than one transcript under Pb stress, and different transcripts had different responses to Pb. By analyzing the expression profiles of at 9 Pb stress time points, 41 of 53 were found to be significantly responsive to Pb. Short time-series expression miner (STEM) analysis revealed that 41 had two significant Pb positive response patterns (early and late), both containing 10 . The with the most significant Pb response were mainly from the ATAF and NAP subfamilies. Therefore, 4 and 3 from the ATAF and NAP subfamilies, respectively, were selected as candidate Pb-responsive for further structural and functional analysis. The RT-qPCR results of 7 transcripts also confirmed the different Pb response patterns of the ATAF and NAP subfamilies. SiNAC004 and SiNAC120, which were randomly selected from two subfamilies, were confirmed to be nuclear localization proteins by subcellular localization experiments. Functional prediction analysis of the associated transcripts of seven candidate showed that the target pathways of ATAF subfamily SiNACs were "sulfur metabolism" and "glutathione metabolism", and the target pathways of NAP subfamily SiNACs were "ribosome" and "phenylpropanoid biosynthesis". This study not only identified two NAC subfamilies with different Pb response patterns but also identified Pb-responsive that could provide a basis for subsequent gene function verification.