Plasma membrane-associated abscisic acid (ABA) signal transduction is an integral part of ABA signaling. The C2-domain ABA-related (CAR) proteins play important roles in the recruitment of ABA receptors to the plasma membrane to facilitate ABA signaling. However, how CAR proteins are regulated remains unclear. In this study, we conducted a genetic screen for mutants with altered leaf transpiration and identified an uncharacterized protein, LOWER TEMPERATURE 1 (LOT1), which regulates the dynamic localization and stability of CAR proteins. The lot1 mutant had a lower leaf temperature as compared with the wild type due to higher transpiration. We found that LOT1 physically interacts with CAR9 , and ABA reduces LOT1–CAR9 interaction in the nucleus, likely via Ca²⁺, resulting in increased localization of CAR9 to the plasma membrane. We further found that the stability of CAR9 is affected by LOT1 less CAR9 proteins were accumulated and more were ubiquitinated in lot1. While the lot1, car9 and lot1 car9 mutants were hyposensitive to ABA, the hyposensitive phenotype of lot1 could be rescued by CAR9 overexpression. Collectively, our study reveals that LOT1 regulates plant tolerance to drought stress by affecting ABA signaling through regulating the stability and dynamic localization of CAR9.

质膜相关脱落酸（ABA）信号转导是ABA信号的组成部分。C2域ABA相关（CAR）蛋白在将ABA受体募集到质膜以促进ABA信号传导中起重要作用。然而，如何调节CAR蛋白尚不清楚。在这项研究中，我们进行了具有突变的叶片蒸腾作用的突变体的遗传筛选，并鉴定了一个未表征的蛋白LOWER TEMPERATURE 1（LOT1），该蛋白可调节CAR蛋白的动态定位和稳定性。所述LOT1突变体具有较低的叶片温度与野生型相比，由于较高的蒸腾。我们发现LOT1与CAR9发生物理相互作用，而ABA可能通过Ca ²⁺降低了LOT1–CAR9在细胞核中的相互作用。，导致CAR9在质膜上的定位增加。我们进一步发现，LOT9影响CAR9的稳定性，在lot1中积累的CAR9蛋白较少，泛素化程度更高。虽然LOT1，car9和LOT1 car9突变体hyposensitive到ABA，的hyposensitive表型LOT1可以通过CAR9表达救出。总体而言，我们的研究表明，LOT1通过调节CAR9的稳定性和动态定位来影响ABA信号传导，从而调节植物对干旱胁迫的耐受性。