CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
BMC Biol. 2021 Nov 23;19(1):249. doi: 10.1186/s12915-021-01177-z.
Diatoms usually dominate phytoplankton blooms in open oceans, exhibiting extremely high population densities. Although the iron uptake rate of diatoms largely determines the magnitude and longevity of diatom blooms, the underlying mechanisms regulating iron uptake remain unclear.
The transcription of two iron uptake proteins, ISIP2a and ISIP1, in the marine diatom Phaeodactylum tricornutum was enhanced with increasing cell density, whereas the cellular iron content showed the opposite trend. When compared with the wild-type strain, knockdown of ISIP2a resulted in 43% decrease in cellular iron content, implying the involvement of ISIP2a in iron uptake under high-cell density conditions. Incubation of the diatom cells with sonicated cell lysate conditioned by different cell densities did not affect ISIP2a and ISIP1 expression, ruling out regulation via chemical cues. In contrast, ISIP2a and ISIP1 transcription were strongly induced by red light. Besides, chlorophyll fluorescence excited from the blue light was also positively correlated with population density. Subsequently, a "sandwich" illumination incubator was designed to filter out stray light and ensure that the inner layer cells only receive the emitted chlorophyll fluorescence from outer layers, and the results showed that the increase in outer cell density significantly elevated ISIP2a and ISIP1 transcription in inner layer cells. In situ evidence from Tara oceans also showed positively correlated between diatom ISIP transcripts and chlorophyll content.
This study shows that chlorophyll fluorescence derived from neighboring cells is able to upregulate ISIP2a and ISIP1 expression to facilitate iron assimilation under high-cell density. These results provide novel insights into biotic signal sensing in phytoplankton, which can help to elucidate the underlying mechanisms of marine diatom blooms.
硅藻通常在开阔海域的浮游植物爆发中占主导地位，表现出极高的种群密度。尽管硅藻的铁吸收速率在很大程度上决定了硅藻爆发的规模和持续时间，但调节铁吸收的潜在机制仍不清楚。
海洋硅藻三角褐指藻中铁吸收蛋白 ISIP2a 和 ISIP1 的转录随着细胞密度的增加而增强，而细胞内铁含量则呈现相反的趋势。与野生型菌株相比，ISIP2a 的敲低导致细胞内铁含量减少 43%，这意味着 ISIP2a 参与了高密度条件下的铁吸收。用不同细胞密度条件下超声处理的细胞裂解液孵育硅藻细胞不会影响 ISIP2a 和 ISIP1 的表达，排除了通过化学信号的调节。相比之下，ISIP2a 和 ISIP1 的转录强烈地被红光诱导。此外，从蓝光激发的叶绿素荧光也与种群密度呈正相关。随后，设计了一种“三明治”光照培养箱来过滤杂散光，确保内层细胞只接收外层细胞发出的叶绿素荧光，结果表明外层细胞密度的增加显著提高了内层细胞中 ISIP2a 和 ISIP1 的转录。从 Tara 海洋获得的原位证据也表明，硅藻 ISIP 转录物与叶绿素含量之间呈正相关。
本研究表明，来自相邻细胞的叶绿素荧光能够上调 ISIP2a 和 ISIP1 的表达，从而促进高密度下的铁同化。这些结果为浮游植物中的生物信号感应提供了新的见解，有助于阐明海洋硅藻爆发的潜在机制。
