Low-Temperature-Induced Changes in Rice Panicle Architectures and Their Robustness in Extremely Cold-Tolerant...

Area of Science:

• Plant Science
• Agricultural Science
• Genetics

Background:

• Low-temperature (LT) stress significantly impacts rice cultivation, especially during reproductive stages, affecting pollen development and yield.
• Understanding the mechanisms of LT tolerance in rice is crucial for breeding resilient varieties, particularly given unpredictable cold waves.
• Previous research has not fully elucidated the molecular basis of LT-induced defects in rice pollen formation.

Purpose of the Study:

• To investigate the effects of LT on panicle architecture and fertility in diverse japonica rice varieties.
• To identify molecular mechanisms underlying LT tolerance and sensitivity during rice reproductive growth.
• To explore the impact of LT on gene expression related to stress response, flowering, and cell cycle in rice.

Main Methods:

• Cultivated 28 japonica rice varieties under controlled LT conditions (19.0 °C and 18.5 °C) throughout reproductive growth.
• Analyzed panicle architecture, spikelet density, and fertility across different LT tolerance levels.
• Performed RNA sequencing on early panicles to assess gene expression patterns, focusing on stress response, flowering, and cell cycle-related genes.

Main Results:

• LT stress induced increased spikelet densities on basal branches in sensitive and moderately tolerant varieties, while extremely tolerant varieties maintained stable panicle architecture.
• RNA sequencing revealed LT-induced expression of stress response genes in all varieties.
• In extremely LT-tolerant variety Tohoku 234, genes involved in flowering (e.g., OsGI, OsTOC1) and sugar metabolism showed stepwise induction with decreasing temperatures, while cell cycle-related genes were stepwise suppressed.

Conclusions:

• LT during early reproductive stages can increase spikelet and anther numbers, potentially reducing pollen formation capacity per anther in susceptible rice varieties.
• Variety-specific gene expression patterns, particularly in flowering and cell cycle regulation, contribute to LT tolerance in rice.
• This study provides valuable insights into the genetic and molecular mechanisms governing rice's response to low-temperature stress.