Sains Malaysiana 50(2)(2021): 327-337

http://dx.doi.org/10.17576/jsm-2021-5002-05

Carotenogenesis in Nannochloropsis oculata under Oxidative and Salinity Stress

(Karotenogenesis dalam Nannochloropsis oculata di bawah Tekanan Oksidatif dan Saliniti)

AISAMUDDIN ARDI ZAINAL ABIDIN^1,2, CHOTIKA YOKTHONGWATTANA³ & ZETTY NORHANA BALIA YUSOF^1,2*

¹Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia

²Laboratory of Marine Biotechnology, Institute of Bioscience, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia

³Department of Biochemistry, Kasetsart University, Bangkok 10900, Thailand

Received: 21 October 2018/Accepted: 20 July 2020

ABSTRACT

Nannochloropsis oculata is a unicellular microalgae which is vastly found throughout the environment and have been widely studied due to its high productivity of secondary metabolites and oil content. It is majorly cultured in the aquaculture sector as fish feed and for industries for its polyunsaturated fatty acids. This work aims to study the impact of salinity and oxidative stress on the expression of carotenoid biosynthesis genes and the accumulation of their products in N. oculata via qPCR and HPLC analyses. Three genes responsible for production of high value carotenoids namely lycopene beta-cyclase (CrTL-B/LCYB), beta-carotene oxygenase (CrTO) and beta-carotene hydroxylase (CrTR) under different stresses and time points were identified and quantified, and the amount of their products namely β-carotene, zeaxanthin, canthaxanthin, and astaxanthin was measured. N. oculata was treated with different concentrations of Cu²⁺ ion (1, 2, and 5 ppm) and NaCl (50, 150, 250 mM) which resembles conditions of oxidative and salinity stress, respectively. RNA and carotenoids extraction, RT-PCR, qPCR and HPLC was carried out in order to identify the correlation of carotenogenesis genes expression with carotenoids production. Under exposure of both treatments, the carotenoids biosynthesis genes were upregulated up to 6-fold compared to control and targeted carotenoids were overexpressed up to 7-fold. Results from this study gave insights which are beneficial in understanding microalgae’s responses towards abiotic stress via the synthesis of carotenoids.

Keywords: Carotenoids; carotenogenesis; Nannochloropsis oculata; oxidative stress; salinity stress

ABSTRAK

Nannochloropsis oculata ialah mikroalga unisel yang banyak ditemui di alam sekitar dan telah dikaji secara meluas kerana produktiviti tinggi metabolit sekunder dan kandungan minyaknya. Kebanyakannya digunakan di dalam sektor akuakultur sebagai makanan ikan dan di dalam sektor industri untuk asid lemak tak tepu. Kajian ini bertujuan untuk melihat kesan saliniti dan tekanan oksidatif pada pengekspresan gen biosintesis karotenoid dan pengumpulan kandungan karotenoid dalam N. oculata melalui qPCR dan analisis HPLC. Pengekspresan tiga gen yang bertanggungjawab untuk menghasilkan karotenoid bernilai tinggi iaitu beta-siklase likopin (CrTL-B / LCYB), beta-karoten oksigen (CrTO) dan beta-karoten hidroksilase (CrTR) telah dianalisa di bawah tekanan yang berbeza dan jumlah penghasilan produk akhir iaitu β-karoten, zeaxantin, cantaxantin dan astaxantintelah diukur. N. oculata telah dirawat dengan kepekatan ion Cu²⁺ yang berbeza (1, 2 dan 5 ppm) dan NaCl (50, 150, 250 mM) yang menyerupai keadaan tekanan oksidatif dan salin. Pengekstrakan RNA dan karotenoid, RT-PCR, qPCR dan HPLC dilakukan untuk mengenal pasti korelasi ekspresi gen carotenogen dengan pengeluaran karotenoid. Di bawah pendedahan kedua-dua tekanan, pengekspresan gen biosintesis karotenoid telah meningkat sehingga 6 kali ganda berbanding dengan kawalan dan karotenoid yang dihasilkan meningkat sehingga 7 kali ganda. Keputusan daripada kajian ini memberikan pandangan yang bermanfaat dalam memahami tindak balas mikroalga terhadap tekanan abiotik melalui sintesis karotenoid.

Kata kunci: Karotenoid; karotenogenesis; Nannochloropsis oculata; tekanan oksidatif; tekanan saliniti

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*Corresponding author; email: zettynorhana@upm.edu.my