Dr Purva KariaThe 2021 Ragai Ibrahim Award for best student paper in plant biology was awarded to CSB graduate Dr Purva Karia by the Canadian Society for Plant Biology (CSPB). . Karia’s award-winning research in Prof Keiko Yoshioka’s lab identified key molecular changes responsible for regulating senescence-related programmed cell death in plants. Dr Karia says ”I’m honored to receive this recognition by CSPB! Thanks to Keiko Yoshioka for the nomination.”

Programmed cell death is initiated in individual cells within a leaf by the active and highly regulated process of leaf senescence. Initiation of leaf senescence occurs naturally by aging, as when leaves turn yellow during autumn.

Senescence can also be induced by a range of external factors such as drought or darkness. This response is mediated by hormones including abscisic acid (ABA). Karia’s studies have revealed a molecular switch to prevent untimely aging which has potential for improving crop yields.

Karia showed that the TTM1 protein, which is localized in the mitochondrial outer membrane, plays an important role in senescence-associated cell death. Her experiments demonstrate that plants lacking TTM1 have delayed natural and ABA-induced senescence, indicating that TTM1 has a universal role as a positive regulator of senescence-related programmed cell death.

A number of TTM1 phosphorylation sites were published in phosphoprotemics studies, but Karia’s work revealed the biological significance of TTM1 phosphorylation. Testing senescence cues including ABA and darkness demonstrated that TTM1 undergoes phosphorylation events at three major sites. Upon perception of senescence cues, multiple MAP kinases phophorylate TTM1, which in turn regulates TTM1 function and turnover.

Karia made specific changes to TTM1 that mimic or block phosphorylation and observed changes in senescence. Karia says “I’m amazed that plants are smart enough to determine in such a fine-tuned manner when it is time to age. It’s impressive that even a minor tweak in phosphorylation can cause changes in aging.”

This result reveals a novel link between ABA, mitochondria, and programmed cell death in plants via TTM1. This opens up a new direction to establish the role of mitochondria in the execution of programmed cell death during the process of senescence and provide a target mechanism for improving drought resistance.

Professor Ragai Ibrahim established his named CSPB award to recognize excellence in research publication by plant biology students. Karia’s award-winning paper in The Plant Journal is titled “Multiple phosphorylation events of the mitochondrial membrane protein TTM1 regulate cell death during senescence”. Congratulations!

Karia is now leading the Sorghum Metabolic Atlas project at Carnegie Science in Stanford, California for her post-doctoral research. Sorghum is a drought resistant crop and by linking the location of metabolic enzymes to their function, Karia and lab head Prof Sue Rhee hope to be able to transfer drought resistant capabilities to other crop plants.