Effects of increasing light intensities on the cell growth and the RNA m6A upstream regulatory factors in a strain of Alexandrium pacificum

Alexandrium pacificum (Alexandrium sp. qd1) is representative of dinoflagellates that cause harmful red tides, and light intensity is an important factor affecting photosynthetic growth of A. pacificum in red tide outbreaks. N⁶ methyladenosine (m⁶A) RNA modification, as an important post-transcriptional molecular regulatory mechanism, may play an important role in the regulation of photosynthetic growth of dinoflagellates, which are known to exhibit minimal transcriptional regulation. In this study, the growth, photosynthesis, and cell sizes of A. pacificum under increasing light-intensity conditions (30, 100, 200, 300, 400 μmol photons m⁻²s^−l) were examined. It was shown that 30 to 300 μmol m⁻²s^−l light intensity gradually promoted the growth of algal cells in the logarithmic growth phase, whereas 400 μmol m⁻²s^−l induced growth photoinhibition. The growth, photosynthetic indicators, and cell size of A. pacificum were significantly affected by light intensity. Meanwhile, the m⁶A modification level within the light-promoted growth range was detected and its correlation with growth indicators was analyzed. It was found that the m⁶A modification level decreased with the increase in light intensity and it has correlation with μ_max, Fv/Fm, NPQ, and cell size. Then, the members of the upstream regulatory factors of m⁶A modification were identified and characterized. Most m⁶A important writers (MT-A70, WTAP), eraser (ALKBH1/3/5/6/8), and readers (YTH, eIF3C/D/G, hnRNPA2B1/C) were present in A. pacificum. The gene and protein expression of multiple members were detected, and multiple m⁶A modification regulators were found to respond to changes in light intensity. The results showed that m⁶A modification may play an important regulatory role in the growth of A. pacificum under different light-intensity conditions. This study provided some basis and insights for studying the growth regulation of red tide A. pacificum from the aspect of epi‑transcriptome (post transcriptional modifications on RNA).