Comprehensive expression profiling of rice grain filling-related genes under high temperature using DNA microarray

Area of Science:

• Plant Physiology
• Molecular Biology
• Agricultural Science

Background:

• High temperatures during grain filling can impair rice quality and yield.
• Understanding the molecular mechanisms underlying heat stress effects on rice is crucial for developing resilient cultivars.

Purpose of the Study:

• To investigate the impact of high temperature on metabolic pathways during rice grain filling.
• To identify key genes and biochemical changes associated with heat-induced grain chalkiness and reduced weight.

Main Methods:

• Rice caryopses were subjected to high temperature (33°C/28°C) or control temperature (25°C/20°C) during the milky stage.
• Gene expression was analyzed using DNA microarrays and RT-PCR.
• Starch composition, protein accumulation, and grain appearance were assessed biochemically and visually.

Main Results:

• High temperature downregulated starch synthesis genes (e.g., GBSSI, BEIIb) and upregulated starch-degrading enzymes (e.g., alpha-amylases).
• Grains exhibited reduced amylose, altered amylopectin structure (long chain enrichment), decreased storage protein (13-kD prolamin), lower weight, and increased chalkiness.
• Chalkiness severity correlated with amylopectin long-chain enrichment, but varietal differences in chalkiness were not directly linked to amylose or amylopectin structure.

Conclusions:

• High temperature disrupts rice grain metabolism by repressing starch synthesis and promoting degradation, leading to altered starch structure and reduced grain filling.
• Changes in amylopectin structure are implicated in heat-induced grain chalkiness, while varietal differences in chalkiness may involve other mechanisms.
• These findings provide insights into rice quality deterioration under heat stress and potential targets for breeding.