The Sweet Potato NAC-Domain Transcription Factor IbNAC1 Is Dynamically Coordinated by the Activator IbbHLH3 and the Repressor IbbHLH4 to Reprogram the Defense Mechanism against Wounding

Abstract

IbNAC1 is known to activate the defense system by reprogramming a genetic network against herbivory in sweet potato. This regulatory activity elevates plant defense potential but relatively weakens plants by IbNAC1-mediated JA response. The mechanism controlling IbNAC1 expression to balance plant vitality and survival remains unclear. In this study, a wound-responsive G-box cis-element in the IbNAC1 promoter from -1484 to -1479 bp was identified. From a screen of wound-activated transcriptomic data, one transcriptional activator, IbbHLH3, and one repressor, IbbHLH4, were selected that bind to and activate or repress, respectively, the G-box motif in the IbNAC1 promoter to modulate the IbNAC1-mediated response. In the early wound response, the IbbHLH3-IbbHLH3 protein complex binds to the G-box motif to activate IbNAC1 expression. Thus, an elegant defense network is activated against wounding stress. Until the late stages of wounding, IbbHLH4 interacts with IbbHLH3, and the IbbHLH3-IbbHLH4 heterodimer competes with the IbbHLH3-IbbHLH3 complex to bind the G-box and suppress IbNAC1 expression and timely terminates the defense network. Moreover, the JAZs and IbEIL1 proteins interact with IbbHLH3 to repress the transactivation function of IbbHLH3 in non-wounded condition, but their transcription is immediately inhibited upon early wounding. Our work provides a genetic model that accurately switches the regulatory mechanism of IbNAC1 expression to adjust wounding physiology and represents a delicate defense regulatory network in plants.

ZmbHLH80 and ZmbHLH90 transcription factors act antagonistically and contribute to regulatePEPC1cell‐specific gene expression in maize

“…For example, in Arabidopsis, a positive regulator, Enhanced Em level (EEL) and a negative regulator, ABA‐INSENSITIVE 5 (ABI5), regulate expression of one of the late embryogenesis‐abundant ( LEA ) genes, AtEm1 , through a competitive binding to the same cis ‐element (Bensmihen et al ., ). In sweet potato, TFs competitive binding to the same cis ‐element is involved in plant defence against herbivory (Chen et al ., ). In response to wounding, the IbbHLH3 homodimer activates the defence network through direct binding and activation of IbNAC1 gene expression.…”

“…In response to wounding, the IbbHLH3 homodimer activates the defence network through direct binding and activation of IbNAC1 gene expression. To terminate the response, IbbHLH3–IbbHLH4 heterodimer, which downregulates IbNAC1 expression, competes with the IbbHLH3 homodimer for binding to the same cis ‐element within IbNAC1 promoter (Chen et al ., ). ZmbHLH80 and ZmbHLH90 may function in a similar way.…”

Genome-Wide Analysis of the NAC Transcription Factor Gene Family Reveals Differential Expression Patterns and Cold-Stress Responses in the Woody Plant Prunus mume

“…Many studies have shown that NAC proteins are widely involved in various signaling pathways [ 10 , 11 ], growth and development [ 5 , 12 , 13 ] and senescence [ 11 , 14 , 15 ], in response to hormones [ 11 , 16 ] and biotic [ 17 , 18 , 19 , 20 ] and abiotic stress [ 21 , 22 , 23 ]. For instance, NAM gene from petunia determines the positions of meristems [ 13 ].…”

MicroR408 regulates defense response upon wounding in sweet potato

“…Sweet potato is one of the most important food crops with high resistance to stress, especially wounding. Several researchers indicated that multiple transcriptional regulations are activated against wounding in sweet potato (Lin et al, 2012, 2013, 2014; Chen et al , 2016a, b; Li et al , 2016). In this study, we further investigate the wound-repressible miRNAs in sweet potato.…”