The exocyst subunits OsEXO70L2 and OsSEC3A regulate root development through modulating OsPIN1a/b-mediated auxin distribution in rice.

Abstract

Exocyst complex-mediated vesicle trafficking is essential for plant growth and development, yet its roles in crop root development remain poorly understood. Previously, we showed that mutation of the exocyst subunit encoded gene <i>OsEXO70L2</i> leads to reduced root length in the <i>short-root 1</i> (<i>sr1</i>) mutant, but the underlying mechanism was unclear. Here, we demonstrate that OsEXO70L2 interacts with another exocyst subunit, OsSEC3A. The <i>OsSEC3A</i> knockout mutant <i>sec3a-1</i> exhibits shortened roots, a reduced root apical meristem, and vesicle trafficking defects, with phenotypes weaker than those of <i>sr1</i>. The <i>sr1 sec3a-1</i> double mutant resembles <i>sr1</i>, indicating that OsEXO70L2 and OsSEC3A act in the same pathway. Both <i>sr1</i> and <i>sec3a-1</i> show reduced sensitivity to exogenous indole-3-acetic acid and the auxin transport inhibitor 1-naphthylphthalamic acid, accompanied by disrupted auxin distribution in the root tips. OsEXO70L2 and OsSEC3A regulate the plasma membrane abundance and localization of the auxin efflux carriers OsPIN1a/b. Consistently, the <i>ospin1a ospin1b</i> double mutant displays more severe short-root phenotypes and auxin distribution defects, confirming OsPIN1a/b as downstream targets. This study elucidates that OsEXO70L2 and OsSEC3A control root length by regulating vesicle trafficking-dependent OsPIN1a/b localization and auxin distribution in the root tips.