ArHDZ19 contributes to drought tolerance by advancing flowering time in Anoectochilus roxburghii

The homeodomain-leucine zippper gene family encodes plant-specific transcription factors that not only affect growth and development, but also play important roles in the drought response. ArHDZ19, from Anoectochilus roxburghii, encodes a homeodomain-leucine zipper III subfamily protein whose function and molecule ar mechanism remains unclear. Here, we explored the function of ArHDZ19 in regulating growth and the drought response. ArHDZ19 localized in the nucleus and its expression was strongly induced under drought stress. Overexpression of ArHDZ19 in Arabidopsis thaliana (OE-ArHDZ19) not only increased plant height and the length of stamens and pistils, but also resulted in an earlier flowering phenotype. The flowering-related genes FLOWERING LOCUS T (FT), SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1), CONSTANS (CO), FLOWERING LOCUS C (FLC), and GIGANTEA (GI) were up-regulated in the OE-ArHDZ19 lines. Moreover, under drought conditions, overexpression of ArHDZ19 improved the plant survival rate and advanced the flowering time. Stress-responsive genes such as COLD-REGULATED 47 (COR47), KINESIN 1 (KIN1), and RESPONSE TO DESICCATION (RD29A) were up-regulated by drought treatment; however, their transcript levels were lower in OE-ArHDZ19 plants than in wild-type plants. These results indicate that ArHDZ19 can improve the drought resistance of plants by advancing the flowering time, which may be a drought-avoidance mechanism.