Abstract
Cell division requires spatial coordination to properly position the division plane. How division plane positioning contributes to plant growth remains unknown. Two unrelated microtubule binding proteins, TANGLED1 (TAN1) and AUXIN-INDUCED-IN-ROOT-CULTURES9 (AIR9), are together required for normal Arabidopsis growth and division. tan1 air9 double mutants have synthetic growth and division plane orientation defects while single mutants lack obvious defects. We show that the first 132 amino acids of TAN1 (TAN11-132) rescue the tan1 air9 double mutant and localize to the division site during telophase. Loss of both rescue and division-site localization occurred when interaction between TAN1 and PHRAGMOPLAST ORIENTING KINESIN1 (POK1) was disrupted by replacing six amino acid residues with alanines in TAN11-132. However, full-length TAN1 with the same alanine substitutions significantly rescued the tan1 air9 double mutant and remained at the division site throughout mitosis, although its accumulation was reduced and phragmoplast positioning defects occurred. POK1 often fails to accumulate at the division site in tan1 air9 mutants, suggesting that both TAN1 and AIR9 stabilize POK1 there. Finally, a mitosis specific promoter driving TAN1 rescued the tan1 air9 double mutant phenotypes indicating that defects seen in the root differentiation zone reflect the loss of mitotic-specific TAN1 activity.
One sentence summary Specific amino acids within TAN1 are required for its correct localization and function partially through interaction with POK1; both TAN1 and AIR9 mediate POK1 division site localization.