Abstract
Drought limits crop performance worldwide. Plant roots' ability to grow toward moisture, termed hydrotropism, is considered one strategy for optimizing water recruitment from the growth medium. Based on the sequence of the hydrotropism-indispensable MIZ1 protein in Arabidopsis thaliana, we identify hydrotropism and drought-responsive genes in tomato. We utilized CRISPR/Cas9 genome-editing technology for targeted mutagenesis of three hydrotropism-associated loci (MIZ1-like) in tomato (Solanum lycopersicum). We show that the three tomato MIZ1-like genes are drought-responsive and two of them are hydrostimulation-responsive. Examination of the root hydrotropic response of triple and double mutants indicated the gene SlMIZ1-1 as indispensable for tomato root hydrotropism. Moreover, expression of the SlMIZ1-1 gene in the Arabidopsis miz1 mutant effectively complemented the lost MIZ1 functionality, including root hydrotropic bending and generation of hydrotropic Ca2+ signals. Transcriptome analysis of hydrostimulated tomato root tips under control gravity and continuous clinorotation conditions was performed to identify gravitropism- and hydrotropism-responsive genes. This analysis suggested the involvement of ethylene and ABA signalling in modulating the interplay between hydrotropism and gravitropism. Unveiling the molecular mechanisms that underlie hydrotropism and drought response holds great potential for improving crop performance under limiting water availability due to global climate changes.