# TOGR3, a Proteasome β4 Subunit, Orchestrates Sugar Homeostasis to Trade Off Growth and Thermotolerance in Rice

## TL;DR

The study identifies a rice proteasome subunit, TOGR3, that helps balance plant growth and heat tolerance by regulating sugar levels and stomatal function.

## Contribution

TOGR3 is newly identified as a key regulator of sugar homeostasis and thermotolerance in rice through proteasome-mediated processes.

## Key findings

- TOGR3 regulates sugar-metabolizing enzymes to maintain sugar homeostasis and support growth and leaf cooling.
- TOGR3 and TT1 together enhance heat resistance in rice, suggesting a strategy for crop improvement.
- The togr3 mutant shows poor performance under combined heat and drought stress.

## Abstract

Balancing growth and stress resilience remains a central challenge in breeding stress‐resistant crops. Here, we identify TOGR3 (THERMOTOLERANT GROWTH REQUIRED 3), which encodes the rice 26S proteasome β4 subunit, as a key regulator coordinating these two processes. Ubiquitylome profiling reveals that the TOGR3‐dependent ubiquitin‐proteasome system (UPS) maintains sugar homeostasis by selectively controlling the turnover of sugar‐metabolizing enzymes. This regulation promotes leaf sugar accumulation, which serves dual roles by supplying carbon to sustain growth and by optimizing stomatal development and aperture dynamics to enhance leaf cooling capacity. Together, these mechanisms synergistically promote thermal‐adaptive growth and thermotolerance in rice. Notably, combined overexpression of TOGR3 with the α2 subunit gene TT1 further enhances heat resistance, underscoring the potential of coordinated proteasome subunit engineering for crop improvement. Our findings uncover a regulatory module that fine‐tunes the trade‐off between plant growth and abiotic stress resilience, providing promising molecular targets for breeding climate‐resilient crops.

This study identifies a novel thermoregulatory mechanism in rice: TOGR3 partners with 26S proteasome subunits, including TT1, to drive thermoresponsive ubiquitin–proteasome activity, maintaining sugar homeostasis in stomatal regulation to balance growth and stress resistance. The togr3 mutant shows limited capacity under combined heat–drought stress. TOGR3 also facilitates proteasome self‐recycling to reinforce proteostasis, further enhancing stress adaptation.