AtHsp101 research sets course of action for the genetic improvement of crops against heat stress

Caseinolytic protease (Clp)/Hsp100 proteins are members of the AAA+ (ATPase associated with a variety of cellular activities) family of proteins present in lower life forms and plants. These proteins represent a unique chaperone system that performs the crucial role of retrieving functional proteins from the aggregated state and are thus also referred to as disaggregases. Clp/Hsp100s were originally discovered in bacteria and yeast cells in late 1980s and early 1990s. Arabidopsis thaliana, in particular after the completion of its genome sequencing in the year 2000, has served as an excellent experimental system for investigating this important chaperone machine in plants. From the reverse and forward genetic analysis carried out with Arabidopsis Hsp101, it emerged that this protein is a powerful candidate gene in conferring heat tolerance. Importantly, this protein is implicated with heat tolerance both in vegetative and reproductive stages of the growth and development of Arabidopsis plants. In the data on genetic polymorphism in the amino acid sequence of Arabidopsis Hsp101 across diverse A. thaliana accessions sequenced in 1001 Arabidopsis genome sequencing project, we find that that there are sixty-three distinct AtHsp101 sequence types with variations in N-terminus, nucleotide binding and C-terminus domains in 855 analyzed Arabidopsis accessions. The in-depth analysis with these variant allelic forms may yield invaluable information on genetic variations in the regulatory regions which control the Hsp101 expression as well as those affecting Hsp101 disaggregase activity. Arabidopsis Hsp101 protein has turned out to be a prototype in search for homolog proteins and mechanisms of heat stress tolerance in rice as well as across diverse crops. Herein, we present the status of our understanding on the Arabidopsis Hsp101 genes, proteins, and their functional relevance.