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

The NTL (NAC with transmembrane motif 1-like) transcription factors with a conserved transmembrane motif (TM) are members of the NAC family and are important in plant development and response to stress. However, the knowledge of their regulatory pathways is scarce, especially in heat stress (HS). Here, a novel lily (Lilium longiflorum) NTL, LlNAC014, was cloned and identified that increased thermotolerance. High temperature repressed LlNAC014 expression but activated its protein. LlNAC014 contained a typical TM at its far C-terminal and was normally located on membranes, but with HS, it entered the nucleus as a transcription factor. LlNAC014 had a transactivation domain at its C-terminus, and its active form of removing TM, LlNAC014ΔC, could function as a trans-activator in both yeast and plant cells. LlNAC014ΔC overexpression in lily and Arabidopsis increased thermotolerance and also caused growth defects; but silencing LlNAC014 in lily decreased thermotolerance. LlNAC014ΔC could constitutively activate heat stress response by inducing the expression of heat-responsive genes that were dependent or not on the HSF (heat stress transcription factor) pathway. Further analysis showed 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 expressions. Thus, LlNAC014 increased thermotolerance by sensing high temperature and translocating to the nucleus to activate the DREB2-HSFA3 module.