Plants adapted to different environmental conditions during evolution mostly by altering their physiological processes through gene mutations and modifications. Understanding these evolutionary changes are important as this knowledge can be used to engineer future plants with better and wider adaptability. During photosynthesis, RCA activates Rubisco enzyme by removing the sugar phosphates from the CO2 and the metal binding sites. The inability of RCA to keep pace with faster Rubisco deactivation during heat stress constraints photosynthesis in many important crops including wheat. Rubisco activation and CO2 fixation rate of wheat start to decline even at 30°C and complete photosynthesis inhibition occurs at temperatures above 38°C. Rubisco deactivation temperature and the RCA thermal stability of other species in the same grass family were significantly higher than that of wheat, however, the underlying molecular mechanism is not clear. We performed a comparative sequence analysis to study the evolutionary changes occurred during the divergence of monocots, which determined the gene structure, expression and thermal sensitivity of RCA function in different species. Characterization of Rca genes by cloning in cereal crops showed that a tandem duplication of Rca occurred in a common grass ancestor, probably before the divergence of Poaceae subfamilies. Different insertions and mutations in the promoter and coding sequences in one of the Rca genes appeared to be responsible for its heat induced expression pattern and thermal stability in these heat tolerant cereal crops. Insertion of transposable elements was common in the promoter or intergenic sequences and many of these transposons contained Heat Responsive Elements (HRE). These tandemly duplicated Rca genes are in fate determination phase and evolving differently at a faster rate in all these cereal crops. Additionally, we further extended the Rca gene search in the sequenced genomes of cyanobacteria to higher plants by including some evolutionarily important species of plant kingdom to understand the gene copy number variation, structure, and protein domain evolution. Improving the thermal stability of wheat RCA by using the knowledge from closely related heat adapted crops may help us to engineer heat tolerant wheat cultivars.