“Pinning” down root growth
05 Feb 2016 NUS scientists discover that a plant-type Pin1, Pin1At, a peptidyl-prolyl isomerase, can regulate root growth in response to gravity by mediating a hormone pathway in plants.
Pin1 is an important enzyme that is highly expressed in many human cancers and is suppressed in Alzheimer diseased brains. A team led by Prof LIOU Yih-Cherng from the Department of Biological Sciences (DBS) in NUS has been working on human Pin1 for many years.
The current publication in Nature Communications is a joint effort of two teams, Prof YU Hao’s team and Prof Liou’s team. Prof Yu is an expert in plant development. They started collaborating a couple of years ago to decipher the function of a plant-type Pin1 in plants. They published their first paper together about five years ago, when they discovered for the first time Pin1At as a molecular “switch” that turns on and off the flowering time in the model plant Arabidopsis. The work was published in Mol Cell.
In the current study published in Nature Communications, co-corresponding by Prof Yu and Prof Liou, they uncover another new function of Pin1At in controlling root growth in response to gravity (gravitopism). Understanding root growth in response to gravity has fascinated scientists including KNIGHT and DARWIN since the beginning of the 19th century, because root gravitropism regulates roots to grow downward into the soil to absorb nutrients and water. Later, over 80 years ago, CHOLODNY and WENT hypothesised that plants bend in response to a gravity stimulus by generating a growth regulator at an organ's apex, later found to be auxin. Scientists have known that auxin transport is highly regulated by a group of transporter proteins call PINs, but the detailed mechanism of how this pathway is controlled has not yet been well elucidated. In this study, Prof Yu and Prof Liou’s teams worked together in providing evidence to explain how auxin and PINs are regulated by Pin1At, thus controlling root gravity. As a result, alteration in Pin1At levels greatly affects root gravitropic responses.
The principle functions of roots are not only to anchor plants into soil and support their stems, but also to absorb water, nutrients and minerals. Regulation of root development is essential for almost all plant growth. From previous and current studies, Pin1At is vital in controlling flowering time and root growth. Therefore, understanding how Pin1At functions is crucial for cultivating stronger and/or more fruitful plants.
The researchers believe that Pin1At as a key regulator in the cell signalling pathway may play many other important roles in plants. To move forward, these two teams will continue to work together on Pin1At function in regulating plant development. They hope to extend their knowledge to cultivate stronger, faster-growing and more fruitful crop plants in the near future. For instance, by manipulating Pin1At levels in the roots, they may cultivate some crops that generate stronger and more effective roots. Consequently, these plants can absorb water and nutrients more effectively so that they can survive in extreme and challenging environments where soils contain less moisture and nutrients. The technology can ultimately be utilised in increasing yields for agricultural and horticultural products.
It has been shown that human Pin1 plays a pivotal role in cancer and Alzheimer’s disease, through mediating a reversible Thr\Ser phosphorylation pathway, which is antagonistically regulated by the upstream kinases and a downstream phosphatase PP2A. In plants, they show that a plant-type Pin1, Pin1At plays an important role in controlling flowering time and root growth, sharing a similar reversible Thr\Ser phosphorylation mechanism as seen in mammalian. Thus, their findings suggest that evolutionarily Pin1-like PPIases may share a convergent enzymatic function that catalyses a conformational change of key substrates relevant to reversible protein phosphorylation involving kinases and PP2A in both plants and animals.
Figure shows the root phenotypes of wild-type control plants (A), Pin1At-overexpressed plants (B), Pin1At depleted plants (C). [Image credit: Liou YC]
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