The NAC Transcription Factors CjNAC43 and CjNAC54 Act as Positive Regulators of Leaf Senescence in Clerodendrum japonicum

Leaf senescence is a crucial developmental process in plants, and is tightly regulated by transcription factors such as NAC family members. However, the functions of NAC genes in the leaf senescence of the medicinal and ornamental plant <i>Clerodendrum japonicum</i> remain largely uncharacterized. In this study, we performed the transcriptome sequencing of mature and early-senescent leaves in <i>C. japonicum</i>. We screened candidate NAC genes and validated their expression patterns using quantitative real-time PCR (qRT-PCR). The functions of <i>CjNAC43</i> and <i>CjNAC54</i> were characterized through heterologous overexpression in <i>Arabidopsis thaliana</i> and Virus-Induced Gene Silencing (VIGS) in <i>C. japonicum</i>. We further investigated their roles in abscisic acid (ABA)- and dark-induced senescence. Our findings revealed that transcriptomic analysis identified 522 differentially expressed genes, including nine NAC members. <i>CjNAC43</i> and <i>CjNAC54</i> exhibited significantly upregulated expression during the critical senescence phase (90-130 days). Overexpression of either gene in <i>A. thaliana</i> accelerated leaf senescence, up-regulated senescence-associated genes (<i>SAG</i>s), and reduced chlorophyll content. Conversely, silencing <i>CjNAC43</i> or <i>CjNAC54</i> in <i>C. japonicum</i> delayed senescence. Both genes enhanced the plant's sensitivity to ABA and darkness, leading to accelerated senescence under these stresses. In conclusion, our results demonstrate that <i>CjNAC43</i> and <i>CjNAC54</i> function as positive regulators of leaf senescence in <i>C. japonicum</i>, partly by mediating ABA and dark signaling pathways.