Inhibition of chloroplast translation as a new target for herbicides

The rise in herbicide resistance over recent decades threatens global agriculture and food security and so discovery of new modes of action is increasingly important. Here we reveal linezolid, an oxazolidinone antibiotic that inhibits microbial translation, is also herbicidal. To validate the herbicidal mode of action of linezolid we confirmed its micromolar inhibition is specific to chloroplast translation and did not affect photosynthesis directly. To assess the herbicide potential of linezolid, testing against a range of weed and crop species found it effective pre- and post-emergence. Using structure-activity analysis we identified the critical elements for herbicidal activity, but importantly also show, using antimicrobial susceptibility assays, that separation of antibacterial and herbicidal activities was possible. Overall these results validate chloroplast translation as a viable herbicidal target.

Inhibition of chloroplast translation as a new target for herbicides

The rise in herbicide resistance over recent decades threatens global agriculture and food security and so discovery of new modes of action is increasingly important. Here we reveal linezolid, an...

Functional Analysis of PSRP1, the Chloroplast Homolog of a Cyanobacterial Ribosome Hibernation Factor

Bacterial ribosome hibernation factors sequester ribosomes in an inactive state during the stationary phase and in response to stress. The cyanobacterial ribosome hibernation factor LrtA has been suggested to inactivate ribosomes in the dark and to be important for post-stress survival. In this study, we addressed the hypothesis that Plastid Specific Ribosomal Protein 1 (PSRP1), the chloroplast-localized LrtA homolog in plants, contributes to the global repression of chloroplast translation that occurs when plants are shifted from light to dark. We found that the abundance of PSRP1 and its association with ribosomes were similar in the light and the dark. Maize mutants lacking PSRP1 were phenotypically normal under standard laboratory growth conditions. Furthermore, the absence of PSRP1 did not alter the distribution of chloroplast ribosomes among monosomes and polysomes in the light or in the dark, and did not affect the light-regulated synthesis of the chloroplast psbA gene product. These results suggest that PSRP1 does not play a significant role in the regulation of chloroplast translation by light. As such, the physiological driving force for the retention of PSRP1 during chloroplast evolution remains unclear.

Dual-targeted transcription factors are required for optimal photosynthesis and stress responses in Arabidopsis thaliana

SummaryChloroplast to nucleus retrograde signaling is essential for cell function, acclimation to fluctuating environmental conditions, plant growth and development. The vast majority of chloroplast proteins are nuclear-encoded and must be imported into the organelle after synthesis in the cytoplasm. This import is essential for the development of fully functional chloroplasts. On the other hand, functional chloroplasts act as sensors of environmental changes and can trigger acclimatory responses that influence nuclear gene expression. Signaling via mobile transcription factors (TFs) has been recently recognized as a way of communication between organelles and the nucleus. In this study, we performed a targeted reverse genetic screen to identify novel dual-localized TFs involved in chloroplast retrograde signaling during stress responses. We found that CHLOROPLAST IMPORT APPARATUS 2 (CIA2), a TF with putative plastid transit peptide can be detected in chloroplasts and the nucleus. Further, we found that CIA2, along with its homolog CIA2-like (CIL) act in an unequally redundant manner and are involved in the regulation of Arabidopsis responses to UV-AB, high light, and heat shock. Finally, our results suggest that both CIA2 and CIL are crucial for chloroplast translation. Our results contribute to a deeper understanding of signaling events in the chloroplast-nucleus cross-talk.SignificanceWe found that a transcription factor CIA2 can be located in chloroplasts and nucleus. CIA2 and is close homolog CIL are involved in protein translation and abiotic stress responses, and we suggest that they play an essential role in retrograde signaling between these organelles.