Title：
Genetic transformation of the microalgal parasite Paraphysoderma sedebokerense enables direct visualization of its pathogenic interaction with Haematococcus pluvialis
Authors：
Corresponding
Author：
Wenjie Tian, Pieter van West, Shiyuan Zhao, Xiaobin Wen, Zhongjie Wang, Yeguang Li, Yi Ding*
Pubyear：
2026
Title of
Journal：
Algal Research-Biomass Biofuels and Bioproducts
Paper
Code：
Volume：
96
Number：
Page：
96:104730
Others：
Classification：
Source：
Abstract：
Paraphysoderma sedebokerense is a parasitic blastoclad fungus that threatens the commercial cultivation of Haematococcus pluvialis, the primary source of natural astaxanthin. However, the absence of genetic tools has hindered the molecular studies of pathogenesis of this pathogen and slowed the progress of disease control in microalgal cultivation. Here, we isolated a P. sedebokerense strain from infected H. pluvialis cultures and developed the first stable Agrobacterium tumefaciens-mediated transformation system for this pathogen. Motile zoospores were identified as optimal recipients, and co-cultivation with A. tumefaciens in pre-formed depressions enabled efficient genetic transformation. The cauliflower mosaic virus 35S promoter effectively drove stable GFP and hygromycin resistance gene expression, as confirmed by PCR and Southern blotting, which revealed singlecopy insertions. The transformants maintained wild-type colony morphology, sporangium development, and infectivity towards host H. pluvialis. Importantly, the clear distinction between the GFP signal and host red autofluorescence enabled direct visualization of the infection progress, revealing multi-site invasion of microalgal cells and progression of the parasitic life cycle. In addition, our observations further confirmed and provided clear visualization that P. sedebokerense specifically infected both green and red immotile cell stages of H. pluvialis. This is the first study to develop a genetic transformation system for examining microalgal fungal pathogens. Beyond enabling functional dissection of host-pathogen interactions, it provides a practical framework for the development of genetic tools for other zoosporic fungi associated with microalgal diseases and opens new avenues for elucidating the molecular basis of pathogenesis and designing targeted strategies to control microalgal diseases.
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