Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2020
Publication Date: 3/4/2020
Citation: Waite, J.M., Collum, T.D., Dardick, C.D. 2020. AtDRO1 is nuclear localized in root tips under native conditions and impacts auxin localization. Plant Molecular Biology. 103:197-210. https://doi.org/10.1007/s11103-020-00984-2.
Interpretive Summary: Currently, it is unknown how plant shoots and roots are able to determine the direction of growth. What we do know is that this unknown mechanism involves the plants ability to sense gravity. We previously identified a gene called Deeper Rooting 1 (DRO1) that controls the growth orientation of plant roots. Over-expression of DRO1 in plum trees led to downward oriented roots and deeper rooting. Despite several attempts by several groups around the world, we show for the first time that the protein encoded by DRO1 is located in the cell nucleus within root tips. This location is different from the root cap where the gene is most active, suggesting that the protein moves from the root cap and into the elongating part of the root. Consistent with other reports, we found that loss of DRO1 impairs the ability of the plant to re-localize the plant hormone auxin – a process essential to gravity response. Yet, DRO1 mutant plants did not have any impairment in gravity responses. Collectively, the results indicated that current models for gravity response in plants may be in error and that the process of establishing root orientation works through a unique mechanism.
Technical Abstract: Deeper Rooting 1 (DRO1) contributes to the downward gravitropic growth trajectory of roots upstream of auxin translocation in monocots and dicots. Loss of DRO1 function leads to horizontally oriented lateral roots and altered gravitropic set point angle, while loss of all three DRO family members results in upward, vertical root growth. These changes are accompanied by a loss of auxin translocation in dro1 mutants and a reversal of the auxin gradient in triple mutants upon gravistimulation. Current evidence suggests DRO1 is a membrane localized protein. Here, we show that VENUS-tagged AtDRO1 driven by the native AtDRO1 promoter complemented an AtDRO1 Arabidopsis mutant and the protein was found to be predominantly nuclear localized in root tips, and in contrast to previous gene expression studies, was largely absent in the root columella. AtDRO1 primary and lateral roots did not establish an auxin gradient upon gravistimulation as visualized with the DII-VENUS reporter. Additionally, PIN3 domain localization was not significantly altered upon gravistimulation in AtDRO1 primary and lateral roots. AtDRO1 lateral root angles were able to respond to exogenous auxin and AtDRO1 gene expression levels in root tips were unaffected by auxin addition. Collectively, the data suggest that nuclear localization is likely important for AtDRO1 function and suggests a more nuanced role for DRO1 in regulating auxin-mediated changes in lateral branch angle.