Recent gene duplication and subfunctionalization produced a mitochondrial GrpE, the nucleotide exchange factor of Hsp70 complex, specialized in thermotolerance to chronic heat stress in ArabidopsisDuplication and divergence of heat stress (HS) response genes might help plants adapt to varied HS conditions, but little is known on the topic. In this study, we examined the evolution and function of Arabidopsis mitochondrial GrpE (Mge) proteins. GrpE acts as a nucleotide exchange factor in the Hsp70/DnaK chaperone machinery. Genomic data show that AtMge1 and AtMge2 arose from a recent whole-genome duplication event. Phylogenetic analysis indicated that duplication and preservation of Mges occurred independently in many plant species, which suggests a common tendency in the evolution of the genes. Intron-retention contributed to the divergence of the protein structure of Mge paralogs in higher plants. In both Arabidopsis and tomato, Mge1 is induced by UV-B and Mge2 by heat, which suggests regulatory divergence of the genes. Consistently, AtMge2 but not AtMge1 is under the control of HsfA1, the master regulator of the HS response. Heterologous expression of AtMge2 but not AtMge1 in the temperature-sensitive E. coli grpE mutant restored its growth at 43 degree C. Arabidopsis T-DNA knockout lines under different HS regimes revealed Mge2 specifically required for tolerating prolonged exposure to moderately high temperature, as compared with the need of Hsp101 and Hsa32 for short-term extreme heat. Therefore, with duplication and subfunctionalization, one copy of the Arabidopsis Mge genes became specialized in a distinct type of HS. Understanding the principle of evolution of HS genes and their role in HS response might be useful in providing guidance in improving heat tolerance of crops.
Co-researchers:Hu C, Lin SY, Chi WT