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PCR test for Okinawa mozuku could increase yields and lead to climate-tolerant strains

PCR test for Okinawa mozuku could increase yield and lead to climate tolerant species

When growing mozuku, germinating “seeds” are grown in flasks and transferred to nets in tanks after budding. The nets are then moved to the ocean where the mozuku grows into mature, edible seaweed. The yield of mozuku changes annually due to cultivation difficulties. Credit: OIST

A simple PCR test could be used to improve cultivation of the edible brown seaweed, Okinawa mozuku, and even in efforts to generate heat-tolerant strains, scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) reported. The PCR test, described in a new study published on June 9, 2022 in Phycological researchdetects nine genes that reveal the life cycle stage of the mozuku algae, as well as its gender.

Okinawa mozuku (Cladosiphon okamuranus) is a beloved algae superfood in Japan, grown by farmers along the Okinawa coast since the 1980s. In the fall, farmers grow mozuku sprouts, or “seeds,” in tanks to induce their buds. Then the farmers take them to the ocean on nets to grow until harvested in the spring. About 15,000 to 20,000 tons of mozuku are collected each year, contributing more than 2 billion yen to the local economy.

However, Mozuku farmers currently face three major problems during the cultivation process. First, some mozuku seeds do not bud. Second, as the mozuku grows in the ocean, it sometimes breaks free from the nets and is swept away by currents and tides. Finally, the seaweed is particularly sensitive to heat, with rising ocean temperatures stunting their growth.

“In 2010, yields dropped to less than half their normal year, which is believed to be due to an unusually warm winter,” said Dr. Koki Nishitsuji, a staff scientist with OIST’s Marine Genomics Unit, led by Professor Noriyuki. sato. “As climate change occurs, the frequency of warmer winters could increase, so new heat-resistant species are needed.”

One of the most effective ways to develop traits such as heat tolerance is through crossbreeding, where individuals of two different species are bred together to create a new mixed species. However, scientists have struggled to cross-breed algae because of difficulties distinguishing male germ cells from female germ cells.

“In other organisms, such as ova and sperm in mammals, there are visible differences,” explains Dr. Nishitsuji out. “But for algae, the germs cannot be identified by eye, only by their DNA.”

PCR test for Okinawa mozuku could increase yield and lead to climate tolerant species

In the mozuku life cycle, germlings occur as haploids and diploids. The sprouts look the same, but farmers only want to grow the diploid sprouts, which will sprout and form mature mozuku. Credit: OIST

In recent years, the Marine Genomics Unit research team has decoded the genomes of the four different S, K, O and C strains of Okinawa mozuku, and the related species Nemacystus decipiens, known as ito-mozuku in Japanese.

Using this wealth of genomic information, the team was able to identify nine key sex-determining genes. When the scientists ran PCR tests on the mozuku germs, five of these genes were detected only in males, while the other four were found only in females.

“Now that we can identify the genus, we have started crossing the O strain with both the S strain and K strain to see if this results in a more heat tolerant strain, Dr. Nishitsuji said. We are also working to identify genes that can act as markers for the different strains so that we can fully confirm that the crosses were successful.”

In addition to introducing heat resistance to newly developed species, crossing could also help the researchers tackle the problem of mozuku being washed away into the sea, developing species of mozuku that adhere more firmly to the nets.

While the PCR test was developed primarily to aid in crossing, the PCR test can also be used by mozuku farmers during the “seeding” stage of cultivation, by allowing them to identify which life cycle stage the seedlings are located.

The life cycle of mozuku is complicated and unique compared to animals and land plants. Humans (and most other animals) are diploid, meaning that our body cells contain two sets of DNA – one set from our mother and another set from our father. Our sex cells (eggs and sperm) are haploid, meaning they have only one set of DNA. At fertilization, the haploid egg and sperm combine to form a diploid embryo.

PCR test for Okinawa mozuku could increase yield and lead to climate tolerant species

PCR tests of diploid, male haploid and female haploid germs have been developed, which improve the efficiency of cultivation and promote crossbreeding attempts. Credit: OIST

However, in mozuku, nucleations occur at two different stages of the life cycle, as haploids and diploids. But only the diploid germs bud and develop into the edible mature mozuku that the farmers want to grow. If the tank is contaminated with haploid germs, less budding will occur, ultimately yielding lower yields of mozuku.

“Diploid sprouts look the same as male and female haploid sprouts, so it’s a common way for farmers to lose yield,” said Dr. Nishitsuji. “But now our early PCR test can be used to check if they are diploid because these germs will contain all nine male and female genes.”

In the fall, the team will work with the Okinawa Prefectural Fisheries and Marine Technology Center in Itoman and Onna Fisheries Cooperative, using the PCR tests to improve their final yield.

Importantly, the sex-determining marker genes identified in this study are likely similar for other brown algae, such as Undaria pinnatifida (wakame in Japanese) and Saccharina japonica (kombu), which are also economically important crops.

Genome study opens the way to sustainable edible seaweed

More information:
Development of DNA markers distinguishing male and female haploid germs of the brown alga, Cladosiphon okamuranus, Phycological research (2022). DOI: 10.1111/PRE.12489

Provided by Okinawa Institute of Science and Technology

Quote: PCR test for Okinawa mozuku may increase yield and lead to climate tolerant species (2022, June 9,), retrieved June 9, 2022 from https://phys.org/news/2022-06-pcr-okinawa-mozuku- yields-climate -tolerant.html

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