Functional evolutionary conservation of genes involved in root hydrotropism between Arabidopsis and tomato
2Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Israel
Hydrotropism, the directional growth of roots towards a water source, is one of the strategies used by plants to obtain water and adapt to water-stress. Using forward genetics, only two genes have been identified to be involved in root hydrotropism by showing no hydrotropic response when mutated. MIZ1, whose protein product has a conserved domain of unknown function named DUF617, and MIZ2, whose mutant is a weak allele of the GDP/GTP exchange factor GNOM. Recently, MIZ1 was found to function as a negative regulator of the ER Ca2+-ATPase isoform ECA1. The ECA1 activity attenuation by MIZ1 is suggested to be responsible for the generation of a long-distance Ca2+ signal in the phloem, necessary for hydrotropism. However, it is unknown whether MIZ1 homologs containing DUF617 in and in other plants also act as Ca2+ regulators, and their potential involvement in stress-responses is yet to be determined.
Targeting the three-closest AtMIZ1 homolog, we successfully established tomato CRISPR/Cas9 mutant lines exhibiting significantly attenuated hydrotropic responses. Moreover, expression of the closest AtMIZ1 tomato homolog, Solyc04g016060, in Arabidopsis miz1 mutants with AtMIZ1’s promoter and terminator, as well as with the constitutive CaMV 35S promoter, successfully rescued the miz1 mutant hydrotropic response. These results indicate functional evolutionary conservation of genes involved in root hydrotropism between Arabidopsis and tomato.
Further research will focus on Ca2+ activity in the tomato and Arabidopsis mutant lines, by imaging cytosolic Ca2+ levels during stress responses, to determine whether the AtMIZ1-tomato closest homologs also regulate Ca2+ signaling activity.