A lily membrane-associated NAC transcription factor LlNAC014 is involved in thermotolerance via activation of the DREB2-HSFA3 module

Heat stress stimulates the transcription factor LlNAC014 to translocate from the membrane to the nucleus, acting as a trans-activator of the DREB2-HSFA3 module to establish thermotolerance in lily. The NTL (NAC with transmembrane motif 1-like) transcription factors with a conserved transmembrane motif are members of the NAC family and are important in plant development and in response to stress. However, knowledge of their regulatory pathways is scarce, especially under heat stress. Here, we cloned and identified a novel lily (Lilium longiflorum) NTL gene, LlNAC014, that increases thermotolerance. High temperature repressed LlNAC014 expression but activated its protein. LlNAC014 contained a typical transmembrane motif at its far C-terminus and was normally located on membranes, but under heat stress it entered the nucleus as a transcription factor. LlNAC014 also has a transactivation domain at its C-terminus, and its active form, LlNAC014 Delta C, could function as a trans-activator in both yeast and plant cells. LlNAC014 Delta C overexpression in lily and Arabidopsis increased thermotolerance, and also caused growth defects; silencing LlNAC014 in lily decreased thermotolerance. LlNAC014 Delta C could constitutively activate the heat stress response by inducing the expression of heat-responsive genes, some of which were dependent on the HSF (heat stress transcription factor) pathway. Further analysis showed that LlNAC014 was a direct regulator of the DREB2-HSFA3 module, and bound to the CTT(N7)AAG element in the promoters of LlHSFA3A, LlHSFA3B, and LlDREB2B to activate their expression. Thus, LlNAC014 increased thermotolerance by sensing high temperature and translocating to the nucleus to activate the DREB2-HSFA3 module.

Automated summary

Heat stress induces the transcription factor LlNAC014 to move from the membrane to the nucleus, acting as a trans-activator of the DREB2-HSFA3 module to enhance thermotolerance in lily. LlNAC014 senses high temperature and translocates to the nucleus to activate the DREB2-HSFA3 module, thereby increasing thermotolerance.