Tissue specificity and responses to abiotic stresses and hormones of PIN genes in rice

The auxin efflux transporter PIN-FORMED (PIN) family is one of the major protein families involved in transporting auxin out of the cell and regulating intracellular auxin homeostasis. However, the tissue-specific expression profiles of OsPIN genes in rice (Oryza sativa) and their expression patterns under abiotic stress and exogenous hormone treatments remain unclear. In this study, a comprehensive tissue-specific expression analysis of OsPIN genes was performed, and the responses of OsPIN genes to diverse abiotic stress (drought, salt and cold) and hormone treatments (abscisic acid, ABA; gibberellin, GA; methyl jasmonate, MeJA and salicylic acid, SA) were further investigated. Six OsPIN genes (OsPIN1a, OsPIN1b, OsPIN5a, OsPIN5b, OsPIN9, and OsPIN10a) showed ubiquitous expression at the seedling and filling stage. Two OsPIN genes (OsPIN2 and OsPIN5c) were expressed predominantly in seedling roots, four OsPIN genes (OsPIN1c, OsPIN1d, OsPIN8 and OsPIN10b) were higher expressed in root-shoot junctions, indicating that OsPIN genes are functionally diverse. OsPIN5b and OsPIN9 were found to respond to all abiotic stress and hormone treatments dramatically in rice seedling roots, indicating that they are potentially involved in the regulation of abiotic stress and hormone signaling to balance plant growth and various exogenous stimuli by guiding auxin flux. Our results provide fundamental insights into the potential regulatory role of OsPIN genes in different tissues and responses to abiotic stress and hormones.