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24.08.2022

+++ News Ticker Science #121 +++ Plant stress +++

Stress-resistant wheat - postulated enzyme activity refuted.

Exposure of crop plants to biotic or abiotic stress often results in yield losses. Making plants more resilient to stress requires a molecular understanding of plant stress responses. In 2014, Chinese researchers found increased tolerance to salts and oxidative stress in the Shanrong 3 variety of bread wheat (Triticum aestivum). In their search for molecular causes for this trait, they discovered the protein variant sro1, which is encoded by an allele that is specific to this wheat variety and - according to the study results at the time - functions as a poly-ADP-ribose polymerase (PARP). PARP enzymes can add poly-ADP ribose chains to target proteins, thereby influencing their function within a signaling cascade such as the stress response. The Chinese researchers reported increased PARP activity of the sro1 protein compared with other PARP variants and, since PARP enzymes are relevant to various stress responses, they postulated a link between the enhanced stress properties of Shanrong 3 and this activity.

However, strikingly, the sro1 protein variant showed significant deviations from the conserved amino acid sequence of PARPs. Therefore, a team of scientists from IPB and FU Berlin recently re-examined the results published 8 years ago. They succeeded in obtaining a crystal structure of the PARP domain of sro1. Structural analysis revealed that although the typical PARP fold is present, crucial conserved residues for the ADP-ribosylation reaction are missing at critical sites of the active site. The scientists then tested whether sro1 could bind the NAD+ co-substrate required for PARPs and catalyze ADP ribosylations. However, both NAD+ binding assays and assays for PARP enzyme activity in vitro and in plant extract were negative.

Based on these results, the research team argues that the stress tolerance of Shanrong 3 wheat is most likely not due to increased PARP activity of the sro1 protein variant. Rather, the wheat variety appears to exhibit altered redox homeostasis, the molecular mechanisms of which need to be elucidated in the future.

Publication:
Sarah Vogt, Karla Feijs, Sebastian Hosch, Raffaella De Masi, Ruth Lintermann, Bernhard Loll, Lennart Wirthmueller, The superior salinity tolerance of bread wheat cultivar Shanrong No. 3 is unlikely to be caused by elevated Ta-sro1 poly-(ADP-ribose) polymerase activity, The Plant Cell, 2022; koac261, https://doi.org/10.1093/plcell/koac261

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