The pepper dehydration-responsive homeobox 1, CaDRHB1, plays a positive role in the dehydration response

Homeobox (HB) genes encode transcription factors that play important regulatory roles in plant growth, development, and plant responses to abiotic stresses, including water deficit. In pepper plant, little is known about HB genes and their functions. Here, we identified 95 putative HB genes within the pepper genome that were classified into 14 classes using phylogenetic analysis. Of the genes responsive to abiotic stresses and ABA treatment, we selected HD ZIP I gene CA08g08650 as a dehydration-responsive homeobox 1 (DRHB1) gene. CaDRHB1-silenced pepper plants exhibited a dehydration-sensitive phenotype, characterized by decreased stomatal closure and high levels of transpirational water loss. CaDRHB1-overexpressing transgenic Arabidopsis plants showed a contrasting opposite phenotype to that of CaDRHB1-silenced pepper plants. Outside of the HD ZIP domain, CaDRHB1 has a serine-rich region (amino acids 8-32) and an AHA motif (amino acids 216-243) which negatively and positively regulate transactivation activity in yeast, respectively. In addition, amino acids 139-190 interact with pepper type 2C protein phosphatases which act as a negative regulator of ABA signaling. Taken together, our findings suggest that CaDRHB1 acts as a positive factor for dehydration tolerance via regulation of ABA-mediated stomatal closure. Moreover, conserved domains may be involved in regulating CaDRHB1 function.