Researchers discover KARAPPO gene
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Researchers discover KARAPPO gene

A cross-institutional research group has revealed the mechanism by which liverwort (Marchantia polymorpha) asexually reproduces via the development of clonal progenies (gemmae). They discovered the gene ‘KARAPPO,’ which is critical for initiating gemma development in liverwort. This research is expected to contribute fundamental knowledge towards technological developments to boost agricultural efficiency.

The collaborative research team consisted of scientists from institutions, including Koyoto University, Kobe University, the National University of Singapore (NUS), and the National Institute for Basic Biology. Members from Kobe University’s Graduate School of Science included Professor Kimitsuke Ishizaki, Yukiko Yasui and Takuma Hiwatashi.

Vegetative reproduction is a form of asexual reproduction in which individual plants are developed directly from the tissues of the parent plant. Liverwort reproduces with the help of vegetative propagation by forming clones of itself (collectively called gemmae) in a gemma cup.

Researchers discover KARAPPO gene- The Idea

These cups from on the thallus, or body, of the plant. Inside the gemma cup, epidermal cells undergo cell elongation followed by two cycles of asymmetrical cell division to form a gemma cell and a basal cell. This gemma cell continues to divide before finally shaping a new plant.

Vegetative reproduction in liverwort Marchantia polymorpha (asexual production of clonal progenies). Credits: https://www.kobe-u.ac.jp

It is thought that bryophytes that include liverworts, mosses, and hornworts evolved from land plants’ algal ancestors more than 430 million years ago. Liverwort was one of the earliest diverging plants to develop characteristics. This allowed them to live on lands. The whole-genome sequence information for liverwort has been available since 2017. The plants carry a minimum set of genetic information. This makes them useful for studying the effects of genetic modification and for helping researchers understand more about the evolution of mechanisms in land plants.

Researchers discover KARAPPO’ gene- The Research Methodology:

The team of scientists focused on two mutant liverworts named karappo-1 and karappo-2. Karappo means empty in the Japanese language. The mutants were given these names for the reason that no initial gemma developed in the cups on these plants.

karappo mutant phenotype Above: Gemma cups as shown through SEM (Scanning Electron Microscope) Below: Cross-section of the gemma cups Scale bar: 100µm. Credits: https://www.kobe-u.ac.jp

Next-generation DNA sequencing of the mutants allowed the researchers to identify the gene responsible for gemmae development- which they named ‘KARAPPO.’

Subsequent analysis of the amino acid sequences of KARAPPO genes showed that the KARAPPO gene encodes the RopGEF. ROP is a type of small GTP-binding protein found in plants. It acts like a ‘switch.’ It signals a range of cellular processes.

ROP activation depends on guanine nucleotide exchange factors (GEFs), which catalyze the release of GDP to facilitate the subsequent binding of GTP in ROP. The RopGEF encoded by KARAPPO was found to trigger cell elongation and asymmetrical cell divisions in the initial stage of gemma development. This showed that the KARAPPO gene is essential in triggering the processes for vegetative reproduction in liverwort

Illustration showing the differences between wild-type liverwort and karappo mutants, and how KARAPPO and RopGEF mediate vegetative propagation. Credits: https://www.kobe-u.ac.jp

Researchers discover KARAPPO’ gene- Conclusion by The Researchers

The study results have illuminated fundamental knowledge regarding vegetative reproduction mechanisms. The findings highlight the importance of the ROP-driven asymmetric division of differentiated cells in land plants.

Further research into these mechanisms could result in revolutionary technological developments in agriculture and biotechnology.

Rahul Mishra is a Science enthusiast and eager to learn something new each day. He has a degree in Microbiology and has joined forces with Biotecnika in 2019 due to his passion for writing and science.