ABA-Mediated ROS in Mitochondria Regulate Root Meristem Activity by Controlling <i>PLETHORA</i> Expression in <i>Arabidopsis</i>

<div><p>Although research has determined that reactive oxygen species (ROS) function as signaling molecules in plant development, the molecular mechanism by which ROS regulate plant growth is not well known. An <i><u>ab</u></i>a <i><u>o</u></i>verly sensitive mutant, <i>abo8-1</i>, which is defective in a pentatricopeptide repeat (PPR) protein responsible for the splicing of <i>NAD4</i> intron 3 in mitochondrial complex I, accumulates more ROS in root tips than the wild type, and the ROS accumulation is further enhanced by ABA treatment. The <i>ABO8</i> mutation reduces root meristem activity, which can be enhanced by ABA treatment and reversibly recovered by addition of certain concentrations of the reducing agent GSH. As indicated by low <i>ProDR5:GUS</i> expression, auxin accumulation/signaling was reduced in <i>abo8-1</i>. We also found that ABA inhibits the expression of <i>PLETHORA1</i> (<i>PLT1</i>) and <i>PLT2</i>, and that root growth is more sensitive to ABA in the <i>plt1</i> and <i>plt2</i> mutants than in the wild type. The expression of <i>PLT1</i> and <i>PLT2</i> is significantly reduced in the <i>abo8-1</i> mutant. Overexpression of PLT2 in an inducible system can largely rescue root apical meristem (RAM)-defective phenotype of <i>abo8-1</i> with and without ABA treatment. These results suggest that ABA-promoted ROS in the mitochondria of root tips are important retrograde signals that regulate root meristem activity by controlling auxin accumulation/signaling and <i>PLT</i> expression in <i>Arabidopsis</i>.</p>