mRNA 5-methylcytidine (m⁵C) modification protects rice against sunburn in hot weather, according to a new study conducted by researchers from Institute of Botany of the Chinese Academy of Sciences.  

This work has been published online in Developmental Cell, in which a methyltransferase OsNSUN2 was identified using molecular genetics and genomics to be responsible for one third of mRNA m⁵C modifications in rice. Gene mutation on OsNSUN2 reduced photosynthesis efficiency and accumulated excessive reactive oxygen species upon heat treatment. Functional defect of this methyltransferase in rice leads to sunburned leaves in summer with a decreased lethal temperature of seedling. Their findings uncovered a novel mechanism that the m⁵C modification on mRNA regulates protein translation in response to higher temperature stress. 

Heat stress primarily attacks photosystem in chloroplast, and consequently light-dependent generation of reactive oxygen species further damage cells.

OsNSUN2 mediated m⁵C modification in mRNA facilitates the translation from mRNAs to proteins. And one third of these proteins are predicted to be finally translocated into chloroplast. The protein synthesis enhancement is primarily beneficial to repair or compensate the deficient components of chloroplast under high-temperature conditions, thus protects rice plants from damaging owing to cytotoxic metabolites generated from impaired chloroplast. 

In the past 140 years, the global surface temperature has increased by 1.5°C. Global warming has already become one of the most serious challenges faced today. Thousands of species are in danger of extinction, because of being unable to adapt to warming climate or lack of enough food. Warming weather not only threatens crop yield, but also changes crop spatial distribution pattern, which could efficiently impact on food supply security.  

The important role of m⁵C modification in maintaining chloroplast function under high-temperature conditions shed light on a new potential way to improve plant thermotolerance in crops.