Arabidopsis ATHB17 coordinates nuclear and plastidic photosynthesis gene expression in response to abiotic stress

Photosynthesis is sensitive to environmental stresses. How nuclear and plastid genome coordinate to cope with abiotic stress is not well understood. Here we report that ATHB17, an Arabidopsis HD-Zip transcription factor, coordinates the expression of nuclear encoded photosynthetic genes (NEPGs) and plastid encoded genes (PEGs) in response to abiotic stress. ATHB17-overexpressing plants display enhanced stress tolerance, whereas its knockout mutant is more sensitive compared to the wild type. Through RNA-seq analysis, we found that ATHB17 down-regulated many NEPGs while up-regulated a number of PEGs. ATHB17 could directly modulate the expression of several NEPGs by binding to their promoters. Furthermore, we identified ATSIG5, encoding a plastid sigma factor, as one of the target genes of ATHB17. Loss of ATSIG5 reduced salt tolerance while overexpression of ATSIG5 enhanced salt tolerance, similar to that of ATHB17. Taken together, our results reveal that ATHB17 is an important coordinator between NEPGs and PEGs partially through ATSIG5 to protect photosynthesis machinery in response to abiotic stresses.