AT5G08670 affects the expression of PhANGs
Mitochondria and chloroplasts are essential for plant growth and development. Plastid development is regulated by the nucleus but also affects nuclear transcriptional activity through plastid feedback by retrograde signaling. Mitochondrial development is also affected by chloroplasts. In rice, a single chloroplast mutation causes inhibition of mitochondrial development (Chen et al., 2018). Therefore, it is possible that mitochondrial gene defects might also affect chloroplast development. AT5G08670 encodes an ATP synthase -subunit in mitochondria. The mitochondrial -subunit is encoded by three genes: AT5G08670 , AT5G08680 , and AT5G08690 (Figure 1a). Only AT5G08670 and AT5G08690 are expressed and they encode an identical mature protein (Figure 1c), implying functional redundancy between these two genes.
The plastid retrograde signaling pathway has been extensively studied, and several mutants with impaired retrograde signaling have been identified in Arabidopsis , such as gun1 , gun4 ,coe1 , and coe2 (Koussevitzky, 2007; Larkin et al., 2003; Sun et al., 2016; Wu et al., 2022). In these mutants PhANGs are significantly expressed in chloroplasts under biotic or abiotic stress, and the normal connection between the chloroplast and nuclear genome is compromised in these mutants (Susek et al., 1993). Expression ofLHCB was higher in the mutant seedlings with a T-DNA insertion inAT5G08670 than in WT seedlings upon LIN and NF treatment (Figure 2a-b), suggesting that AT5G08670 is involved in plastid retrograde signaling. Transcriptome analysis of the AT5G08670mutant revealed that LIN affects the expression of nuclear genes encoding both mitochondrial and chloroplast proteins (Figure 8) raising the possibility that AT5G08670 might be involved in regulating both plastid and mitochondrial retrograde signaling although the mechanisms of mitochondrial regulation of chloroplast development are unknown. However, in maize mutants with defective mitochondrial genes (Gu, Miles, & Newton, 1993; Roussell, Thompson, Pallardy, Miles, & Newton, 1991), the leaves show yellow or pale green stripes indicating that mitochondria affect the development of chloroplasts.