Nature Genet. 47, 827–833 (2015)

Breeding heat-tolerant crops is exceptionally important in the context of global warming. However, our understanding of the genetic basis of plant thermotolerance remains limited. By studying the African rice (Oryza glaberrima) adapted to tropical environments, Xin-Min Li, of the Shanghai Institutes for Biological Sciences, and colleagues uncovered a gene contributing to crop thermotolerance.

Utilizing a segregating population derived from a heat-tolerant African rice accession and a heat-sensitive Asian variety, the researchers narrowed down a major thermotolerant quantitative trait locus, TT1, to a gene encoding a 20S proteasome α2 subunit. Overexpressing TT1 in Asian rice enhances thermotolerance, while silencing this gene causes heat sensitivity. Compared with the Asian allele, the African allele contains several nucleotide substitutions, including an arginine-to-histidine mutation.

Ubiquitylome analyses showed lower accumulation of ubiquitinated proteins in the African genotype during heat stress. Such higher proteasome activity suggests a higher protection against heat stress by eliminating cytotoxic denatured proteins.

Natural variations occurred on both coding and regulatory sequences of the TT1 gene. The African specific haplotype, containing the arginine-to-histidine substitution, shows long-term heat tolerance, Asian varieties exhibit differential TT1 expression, highly correlated with short-term heat tolerance and geographical distribution, suggesting the modulation of TT1 for local adaptation at both protein and mRNA levels.

Introgression of the African TT1 allele into the Asian variety increased yield under heat stress. Transforming this allele in Arabidopsis and tall fescue also enhanced their thermotolerance, showing its potential for breeding heat-tolerant varieties of a wide range of crops.