Coordination of Nuclear and Mitochondrial Genome Expression during Mitochondrial Biogenesis in Arabidopsis

Abstract

Mitochondrial biogenesis and function require the regulated and coordinated expression of nuclear and mitochondrial genomes throughout plant development and in response to cellular and environmental signals. To investigate the levels at which the expression of nuclear and mitochondrially encoded proteins is coordinated, we established an Arabidopsis thaliana cell culture system to modulate mitochondrial biogenesis in response to sugar starvation and refeeding. Sucrose deprivation led to structural changes in mitochondria, a decrease in mitochondrial volume, and a reduction in the rate of cellular respiration. All these changes could be reversed by the readdition of sucrose. Analysis of the relative mRNA transcript abundance of genes encoding nuclear and mitochondrially encoded proteins revealed that there was no coordination of expression of the two genomes at the transcript level. An analysis of changes in abundance and assembly of nuclear-encoded and mitochondrially encoded subunits of complexes I to V of the mitochondrial inner membrane in organello protein synthesis and competence for protein import by isolated mitochondria suggested that coordination occurs at the level of protein-complex assembly. These results further suggest that expression of the mitochondrial genome is insensitive to the stress imposed by sugar starvation and that mitochondrial biogenesis is regulated by changes in nuclear gene expression and coordinated at the posttranslational level.

Oxygen Initiation of Respiration and Mitochondrial Biogenesis in Rice

“…This appears to differ from the situation in yeast, where levels of cox2 are regulated at the translational level under low oxygen conditions (55), but is similar to observations in mammalian cells showing that cox2 transcript levels respond to changes in oxygen availability (56). Furthermore, cox2 protein levels were found to change significantly compared with other mitochondrial encoded proteins in response to sucrose starvation of Arabidopsis cell culture (49), indicating that regulation of cox2 independent of other mitochondrial encoded components exists in other systems.…”

“…2 and 3). Mitochondrial encoded genes are widely considered not to be under transcriptional regulation but instead are regulated by a variety of posttranscriptional events (49,50). Since quantitative reverse transcription-PCR quantifies steady state mRNA levels, which represent the balance between transcription and mRNA stability, it is possible that the stability of the cox2 transcript may be changing in response to oxygen availability, and numerous studies provide evidence for this type of regulation of mitochondrial encoded genes (51)(52)(53)(54).…”

Organelle–nucleus cross-talk regulates plant intercellular communication via plasmodesmata

“…The mitochondrial and plastid genomes encode only a small fraction of the proteins required to perform their essential functions. In A. thaliana, the mitochondrial genome encodes only 33 of the estimated more than 1,000 mitochondrial proteins (56); the remaining mitochondrial proteins are nucleus-encoded and posttranslationally imported into mitochondria. Similarly, the chloroplast imports greater than 95% of the 1,000-3,000 chloroplast proteins (22).…”

Dual Location of the Mitochondrial Preprotein Transporters B14.7 and Tim23-2 in Complex I and the TIM17:23 Complex in Arabidopsis Links Mitochondrial Activity and Biogenesis

“…Mitochondria were isolated as described above and protein synthesis reactions were performed as previously described (Giegé et al, 2005).…”