Ubiquitin facilitates a quality-control pathway that removes damaged chloroplasts

Abstract

Energy production by chloroplasts and mitochondria causes constant oxidative damage. A functioning photosynthetic cell requires quality-control mechanisms to turn over and degrade chloroplasts damaged by reactive oxygen species (ROS). Here, we generated a conditionally lethal Arabidopsis mutant that accumulated excess protoporphyrin IX in the chloroplast and produced singlet oxygen. Damaged chloroplasts were subsequently ubiquitinated and selectively degraded. A genetic screen identified the plant U-box 4 (PUB4) E3 ubiquitin ligase as being necessary for this process. pub4-6 mutants had defects in stress adaptation and longevity. Thus, we have identified a signal that leads to the targeted removal of ROS-overproducing chloroplasts.

EXTRA-LARGE G PROTEINs Interact with E3 Ligases PUB4 and PUB2 and Function in Cytokinin and Developmental Processes

“…The pub4 mutant also shows increased cell proliferation in both shoot apical meristem and root meristem (Kinoshita et al, 2015a(Kinoshita et al, , 2015b. A recent report also shows that PUB4 is involved in individual chloroplast quality control upon oxidative stress (Woodson et al, 2015).…”

Protein Degradation Rate in Arabidopsis thaliana Leaf Growth and Development

“…Ubiquitination plays a role in control of plastids via a RING-type ubiquitin E3 ligase, SP1, which mediates the ubiquitination and degradation of TOC components that are required for developmental transition of plastids (Ling et al, 2012;Huang et al, 2013). Most recently, the plant U-box E3 ligase PUB4 was found to mediate the ubiquitination and selective degradation of damaged chloroplast through globular vacuoles (Woodson et al, 2015). While the proteasome subunit degradation rate was low in young leaves, the degradation rates of three E3 ligases we identified (one RINGtype At1g57800 and two F-box At4g39756 and At5g01720) were higher in younger leaves ( Figure 6E).…”

“…However, plastid turnover is controlled not only by internal proteases but also by the proteasome and vacuolar quality control pathways mediated by E3 (Ling et al, 2012;Woodson et al, 2015). Ubiquitination plays a role in control of plastids via a RING-type ubiquitin E3 ligase, SP1, which mediates the ubiquitination and degradation of TOC components that are required for developmental transition of plastids (Ling et al, 2012;Huang et al, 2013).…”

Mechanism of Dual Targeting of the Phytochrome Signaling Component HEMERA/pTAC12 to Plastids and the Nucleus

“…First, HMR can be retrieved from the plastids by retrograde movement through an unidentified translocon or secretory pathway. Second, HMR can be redistributed as a result of leakage from chloroplasts, either due to organellar damage or during autophagy (Woodson et al, 2015). Because HMRm cannot effectively accumulate in the nucleus, in these two scenarios, HMRm might be modified in plastids to enhance the activity of its own nuclear localization signals or to promote interactions with other proteins that facilitate HMR's nuclear accumulation (Fig.…”