AtHsp70-14 and -15 (At1g79930 and At1g79920) are two closely related isoforms of the Hsp110/SSE subfamily of the HSP70 chaperones in Arabidopsis thaliana. By analysing T-DNA insertion and amiRNA-AtHsp70-14/15 lines, we could demonstrate an essential function of AtHsp70-15 for plant growth. AtHsp70-15 deficient plants are reduced in size and stomata opening is impaired which results in accelerated wilting of detached leaves. Hsp70-15 deficient plants are also more tolerant to TuMV infection but more sensitive to heat treatment. Therefore comparative transcriptome analysis of amiRNA-AtHsp70-14/15, hsp70-14 knockout, hsp70-15 knockout and wild type plants was performed with leaf samples of 6 week old plants grown under ambient conditions. The analysis of differentially regulated genes compared to the wild type Col-0 plants exhibited a constitutive heat stress response / cytosolic protein response of Hsp70-15 deficient plants.