AUTHOR=Yoo Cheol-Min , Blancaflor Elison B.

TITLE=Overlapping and divergent signaling pathways for ARK1 and AGD1 in the control of root hair polarity in Arabidopsis thaliana

JOURNAL=Frontiers in Plant Science

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2013.00528

DOI=10.3389/fpls.2013.00528

ISSN=1664-462X

ABSTRACT=<p>We previously showed that seedlings harboring mutations in genes encoding ARK1, an armadillo repeat-containing kinesin, or AGD1, a class 1 ARF-GAP, have root hairs that exhibit wavy/spiral growth and two tips originating from one initiation site. These root hair defects were accompanied by bundling of endoplasmic microtubules and filamentous actin (F-actin) that extended to the extreme root hair apex. The similar phenotypes of <italic>ark1</italic> and <italic>agd1</italic> mutants suggest a tight coordination between the cytoskeleton and membrane trafficking in the control of root hair polarity. Indeed, cell biological and genetic studies of the <italic>agd1</italic> mutant provided evidence that AGD1's involvement in root hair development involves cross-talk among phosphoinositides (PIs), the actin cytoskeleton and other small GTPases such as ROP2 and RABA4b. Here we show that <italic>ark1</italic> root hairs mirror those of <italic>agd1</italic> with regard to altered targeting of ROP2 and RABA4b, as well as abnormal tonoplast organization. Furthermore, like <italic>agd1</italic>, enhanced root hair defects in double mutants in <italic>ARK1</italic> and genes encoding a type B phosphatidylinositol-4-phosphate 5-kinase 3 (<italic>PIP5K3)</italic>, a phosphatidylinositol-4-phosphate (<italic>PI-4P</italic>) phosphatase (<italic>RHD4</italic>), a phosphatidylinositol transfer protein (<italic>COW1</italic>), and a vegetative actin isoform (<italic>ACT2</italic>), were observed. However, root hair shape of some <italic>ark1</italic> double mutant combinations, particularly those with <italic>act2, pip5k3</italic> and <italic>rhd4</italic> (<italic>ark1 act2</italic>, <italic>ark1 pip5k3</italic>, <italic>ark1 rhd4</italic>), differed in some respects from <italic>agd1 act2, agd1 pip5k3</italic>, and <italic>agd1 rhd4</italic>. Taken together our results continue to point to commonalities between ARK1 and AGD1 in specifying root hair polarity, but that these two modulators of tip-growth can also regulate root hair development through divergent signaling routes with AGD1 acting predominantly during root hair initiation and ARK1 functioning primarily in sustained tip growth.</p>