Deficiency of Auxin Efflux Carrier Impairs Chilling and Drought Tolerance in Rice.

Significant progress has been made in the functions of auxin efflux transporter () genes for the regulation of growth and development in rice. However, knowledge on the roles of genes in abiotic stresses is limited. We previously reported that the mutation of alters rice architecture and root gravitropism, while the role of in the regulation of rice abiotic stress adaptations is still largely elusive. In the present study, two homozygous mutants ( and ) were employed to investigate the roles of in regulating abiotic stress adaptations. Low temperature gradually suppressed expression, while osmotic stress treatment firstly induced and then inhibited expression. Most genes and auxin biosynthesis key genes were up-regulated in leaves, implying that auxin homeostasis is probably disturbed in mutants. The loss of function of significantly decreased rice chilling tolerance, which was evidenced by decreased survival rate, increased death cells and ion leakage under chilling conditions. Compared with the wild-type (WT), mutants accumulated more hydrogen peroxide (HO) and less superoxide anion radicals (O2-) after chilling treatment, indicating that reactive oxygen species (ROS) homeostasis is disrupted in mutants. Consistently, C-repeat binding factor ()/dehydration-responsive element binding factor () genes were downregulated in mutants, implying that genes are implicated in -mediated chilling impairment. Additionally, the mutation of led to decreased sensitivity to abscisic acid (ABA) treatment in seed germination, impaired drought tolerance in the seedlings and changed expression of ABA-associated genes in rice roots. Taken together, our investigations revealed that is implicated in chilling and drought tolerance in rice and provide new insight for improving abiotic stress tolerance in rice.