A novel R2R3-MYB transcription factor LlMYB305 from Lilium longiflorum plays a positive role in thermotolerance via activating heat-protective genes

The R2R3-MYB transcription factors (TFs) have been reported to play important roles in the development, metabolism, and response to abiotic stresses of plants; however, relative to the numerous studies on the involvement of R2R3-MYBs response to drought, salinity, and cold stress, the function of these TFs in heat stress remains largely unknown. Here, we isolated a novel R2R3-MYB, named LlMYB305, from lily (Lilium longiflorum), which was closely related to the AtMYB21 and AtMYB24 of Arabidopsis. The LlMYB305 was induced by high temperature and the protein was primarily located in the nucleus and had transactivation ability in yeast and plant cells. The conserved C-terminal motif of LlMYB305 contributed to its transactivation ability. Overexpression of LlMYB305 caused pronounced growth and fertility defects in transgenic Arabidopsis plants; simultaneously, thermotolerance of the transgenic plants was elevated. The increase in thermotolerance might be due to the up-regulated expression of the heat-protective genes after heat stress treatment, although the genes were not induced and even inhibited under normal conditions in the transgenic plants. Further analysis showed LlMYB305 might be an up-stream regulator of LlHSC70. L1MYB305 repressed the promoter activity of LlHSC70 under normal conditions, but activated the promoter activity under heat stress, which suggested that LlMYB305 might need to be activated by high temperature to take part in the thermotolerance. This study identified an R2R3-MYB member, LlMYB305, from lily, which might play a positive role in thermotolerance.