AUTHOR=Norizuki Takuya , Kanazawa Takehiko , Minamino Naoki , Tsukaya Hirokazu , Ueda Takashi 

TITLE=Marchantia polymorpha, a New Model Plant for Autophagy Studies

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00935

DOI=10.3389/fpls.2019.00935

ISSN=1664-462X

ABSTRACT=<p>Autophagy is a catabolic process for bulk and selective degradation of cytoplasmic components in the vacuole/lysosome. In <italic>Saccharomyces cerevisiae, ATG</italic> genes were identified as essential genes for autophagy, and most <italic>ATG</italic> genes are highly conserved among eukaryotes, including plants. Although reverse genetic analyses have revealed that autophagy is involved in responses to abiotic and biotic stresses in land plants, our knowledge of its molecular mechanism remains limited. This limitation is partly because of the multiplication of some <italic>ATG</italic> genes, including <italic>ATG8</italic>, in widely used model plants such as <italic>Arabidopsis thaliana</italic>, which adds complexity to functional studies. Furthermore, due to limited information on the composition and functions of the <italic>ATG</italic> genes in basal land plants and charophytes, it remains unclear whether multiplication of <italic>ATG</italic> genes is associated with neofunctionalization of these genes. To gain insight into the diversification of <italic>ATG</italic> genes during plant evolution, we compared the composition of <italic>ATG</italic> genes in plants with a special focus on a liverwort and two charophytes, which have not previously been analyzed. Our results showed that the liverwort <italic>Marchantia polymorpha</italic> and the charophytes <italic>Klebsormidium nitens</italic> and <italic>Chara braunii</italic> harbor fundamental sets of <italic>ATG</italic> genes with low redundancy compared with those of <italic>A. thaliana</italic> and the moss <italic>Physcomitrella patens</italic>, suggesting that multiplication of <italic>ATG</italic> genes occurred during land plant evolution. We also attempted to establish an experimental system for analyzing autophagy in <italic>M. polymorpha</italic>. We generated transgenic plants expressing fluorescently tagged MpATG8 to observe its dynamics in <italic>M. polymorpha</italic> and produced autophagy-defective mutants by genome editing using the CRISPR/Cas9 system. These tools allowed us to demonstrate that MpATG8 is transported into the vacuole in an MpATG2-, MpATG5-, and MpATG7-dependent manner, suggesting that fluorescently tagged MpATG8 can be used as an autophagosome marker in <italic>M. polymorpha</italic>. <italic>M. polymorpha</italic> can provide a powerful system for studying the mechanisms and evolution of autophagy in plants.</p>