Methods of increasing the resistance of a crop plant to heat stress and in particular methods of improving the grain yield and quality of crop plants grown under heat stress in the form of increased minimal temperatures are provided. The methods include selecting plants with increased expression of HYR and growing these plants in regions expected to experience minimal temperatures above 25° C. during the growing season. Methods of screening plants for increased resistance to heat stress and methods of producing grain in regions having minimal temperatures of 25° C. or more are also provided.