In Arabidopsis,we screened and isolated a mutant asm1 (ABA sensitive mutant 1,asm1) in the T-DNA mutant library,on ABA medium asm1 was more sensitive to ABA than the wild type on root elongation,further study showed on seed germination asm1 germinated earlier than WT.In terms of growth and development,asm1 exhibited early-flowering and dwarf phenotypes,the size of siliques of the mutants was shorter and more stunted compared with the wild type.Using far infrared imaging system we found that the leaf temperature of asm1 mutant was higher than the wild type under drought stress,water loss rate of mutant was lower and water loss was reduced.Genetic analysis revealed asm1 was a single recessive-gene mutant and cosegregated with a T-DNA tag,We used map-based cloning to identify the candidate gene ASM1.RT-PCR results showed that in the mutant the expression of ASM1 was inhibited,and could regulate expression levels of a variety of ABA signaling and stress response genes.These results indicate that ASM1 may be involved in the regulation of ABA signal transduction and response to drought stress.