The HpGIF1-HpABC44 module facilitates heavy metal detoxification via improved ABA sensitivity and ROS scavenging

ATP-binding cassette (ABC) transporters are known for their roles in detoxification. Although their functions have been elucidated in model plants, the homologs in commercial crops remain unevaluated. Presently, 116 HpABCs were identified in pitaya genome, which can be classified into eight subfamilies, ABCA-G and ABCI. Members from the same subfamily share similar exon-intron structures and conserved motifs. Compared with other plants, HpABCs have undergone purifying selection and the expansion has occurred after the divergence between dicots and monocots. Gene Ontology analysis predicted that most HpABCs are located in membrane system serving as transporters powered by ATP hydrolysis. The analysis of HpABC promoters revealed an abundance of phytohormone- and stress-responsive elements. The RT-qPCR of 12 HpABCs suggested the robust elevation of HpABC44 by heavy metals (HMs), indicating its extensive role in the detoxification. HpABC44-OE Arabidopsis accumulated fewer reactive oxygen species under HM treatments, which can be partially explained by the inhibited ROS biosynthesis and promoted ROS scavenging in the seedlings. Further data showed that stomata in transgenic lines were hypersensitive to exogenous abscisic acid, suggesting less cation uptake by transpiration stream. Yeast one-hybrid and luciferase reporter assays suggested that the HM-induced HpGIF1(Growth-regulating Factor-Interacting Factor1) activated HpABC44 via binding to its promoter. The RT-qPCR showed that HpGIF1 was induced by HMs, especially the Pb and Zn, indicating the activation of HpABC44 by HMs was mediated by HpGIF1. To conclude, this work deepens our understanding on how plants cope with HM and provides insight into the role of pitaya ABC transporters in detoxification.