Transcriptional profiling of Arabidopsis thaliana plants’ response to low relative humidity suggests a shoot–root communication

The creation of a water-stress environment usually starts with a reduction in air relative humidity (RH) while soil water potential still reflects favorable conditions. Arabidopsis plants subjected to low RH (17%) exhibited a significant increase in leaf specific hydraulic conductance, reducing the water potential. However, no detectable effects on stomatal performance or osmotic leaf adjustment were noted relative to plants exposed to high RH. In the present study, we profiled gene expression in roots 2.5 and 5 h after shoot exposure to low RH. Multiple genes with various putative biological roles were identified as differentially expressed under these conditions; among them were aquaporins, some of whose expression was induced under low RH. Transcription of two aquaporin was localized to the roots, especially to cells around the vascular system and to cells of the differentiation zone, and to leaf trichomes. Our results suggest that plant roots perceive the low RH stimulus from shoots through a sensing mechanism(s), leading to distinct plant transcriptional responses, potentially reflecting activation of various biological processes. This activation might be a prelude to the expected forthcoming drought conditions, providing the plant with enhanced resistance to future water-stress situations.