Plastid retrograde signaling plays a key role in coordinating the expression of plastid genes and photosynthesis-associated nuclear genes ( PhANGs). Although plastid retrograde signaling can be substantially compromised by mitochondrial dysfunction, it is not yet clear whether specific mitochondrial factors are required to regulate plastid retrograde signaling. Here, we show that mitochondrial ATP synthase β-subunit mutants with decreased ATP synthase activity are impaired in plastid retrograde signaling. Transcriptome analysis revealed that the expression levels of PhANGs were significantly higher in seedlings affected in AT5G08670, the gene of the β-subunit of mitochondrial ATP synthase than in wild-type (WT) seedlings upon treatment with lincomycin (LIN) and norflurazon (NF). Further studies showed that the expression of nuclear genes involved in chloroplast and mitochondrial retrograde signaling was affected in AT5G08670 mutant seedlings treated with LIN. These changes might be associated with the repression of some transcriptional factors (TFs), such as ARF3/ETTIN ( ETT), PLASTID TRANSCRIPTION FACTOR 1 ( PTF1), CYCLOIDEA AND PCF TRANSCRIPTION FACTOR 2 ( TCP2), and KOW DOMAIN-CONTAINING TRANSCRIPTION FACTOR 1 ( KTF1). These findings indicate that the activity of mitochondrial ATP synthase affects plastid retrograde signaling.

Through crosstalk, FLAGELLIN SENSITIVE 2 (FLS2) and RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD) are involved in regulating the homeostasis of cellular reactive oxygen species (ROS) and are linked to the metabolic response of plants towards both biotic and abiotic stress. In the present study, we examined the metabolome of Arabidopsis seedlings under drought and salt conditions to better understand the potential role of FLS2 and RBOHD-dependent signaling in the regulation of abiotic stress response. We identified common metabolites and genes that are regulated by FLS2 and RBOHD, and are involved in the response to drought and salt stress. Under drought conditions, D-aspartic acid (DAA) and the expression of associated genes, such as ASPARAGINE SYNTHASE 2 ( ASN2), increased in both fls2 and robed/f double mutants. The accumulation of amino acids, carbohydrates, and hormones, such as L-proline, D-ribose, and indoleacetaldehyde increased in both fls2 and rbohd/f double mutants under salt conditions, as did the expression of related genes, such as PROLINE IMINOPEPTIDASE ( PIP), PHOSPHORIBOSYL PYROPHOSPHATE SYNTHASE 5 ( PRS5), and NITRILASE 3 ( NIT3). Collectively, these results indicate that the FLS2-RBOHD module regulates plant response to drought and salt stress through ROS signaling by adjusting the accumulation of metabolites and expression of genes related to metabolite synthesis.