Transcriptome analysis reveals the spatial and temporal differentiation of gene expression in the sporophyte of Undaria pinnatifida

Multicellular organisms are differentiated into specialized organs having specific functions. Kelps, morphologically diverse brown algae of the order Laminariales, exhibit specialized morphological features with a holdfast, a stipe, and a blade. However, little is known about the expression profiles and their biological functions from the different tissues. Among the kelp species, the edible Pacific kelp, Undaria pinnatifida is an ecologically and economically important species native to the Northeastern Asia. It presents the typical organization of kelps but is characterized by the formation of its sporophyll, the sexually reproductive tissue, on the stipe. To study their respective gene expression profiles, we generated transcriptome sequences from four tissues; the sporophyll, meristem, healthy blade, and decaying apex blade were sampled at the three time points in the development of the sporophyte. We demonstrate an up-regulation of genes related to photosynthetic genes in the healthy blade, of genes related to cell proliferation in the meristem and of genes related to flagella development in the sporophyll. Overall, the study revealed clear spatial and temporal variation in the expression patterns within and between the different tissues that were well correlated with the biological functions in the different tissues.