Harnessing Deep Learning to Analyze Cryptic Morphological Variability of Marchantia polymorpha.

Characterizing phenotypes is a fundamental aspect of biological sciences, although it can be challenging due to various factors. For instance, the liverwort Marchantia polymorpha is a model system for plant biology and exhibits morphological variability, making it difficult to identify and quantify distinct phenotypic features using objective measures. To address this issue, we utilized a deep-learning-based image classifier that can handle plant images directly without manual extraction of phenotypic features and analyzed pictures of M. polymorpha. This dioicous plant species exhibits morphological differences between male and female wild accessions at an early stage of gemmaling growth, although it remains elusive whether the differences are attributable to sex chromosomes. To isolate the effects of sex chromosomes from autosomal polymorphisms, we established a male and female set of recombinant inbred lines (RILs) from a set of male and female wild accessions. We then trained deep learning models to classify the sexes of the RILs and the wild accessions. Our results showed that the trained classifiers accurately classified male and female gemmalings of wild accessions in the first week of growth, confirming the intuition of researchers in a reproducible and objective manner. In contrast, the RILs were less distinguishable, indicating that the differences between the parental wild accessions arose from autosomal variations. Furthermore, we validated our trained models by an 'eXplainable AI' technique that highlights image regions relevant to the classification. Our findings demonstrate that the classifier-based approach provides a powerful tool for analyzing plant species that lack standardized phenotyping metrics.

Biosynthesis of riccionidins and marchantins is regulated by R2R3-MYB transcription factors in Marchantia polymorpha.

R2R3-MYB transcription factors constitute the largest gene family among plant transcription factor families. They became largely divergent during the evolution of land plants and regulate various biological processes. The functions of R2R3-MYBs are mostly characterized in seed plants but are poorly understood in non-seed plants. Here, we examined the function of two R2R3-MYB genes of Marchantia polymorpha (Mapoly0073s0038 and Mapoly0006s0226) that are closely related to subgroup 4 of the R2R3-MYB family. We performed LC/MS/MS metabolomics, RNA-seq analysis and expression analysis in overexpressors and knockout mutants of MpMYB14 and MpMYB02. Overexpression of MpMYB14 remarkably increased the amount of riccionidins, which are specific anthocyanins in liverworts and a few flowering plants. In contrast, overexpression of MpMYB02 increased the amount of several marchantins, which are characteristic cyclic bis (bibenzyl ether) compounds in M. polymorpha and related liverworts. Knockouts of MpMYB14 and MpMYB02 abolished the accumulation of riccionidins and marchantins, respectively. The expression of MpMYB14 was up-regulated by UV-B irradiation, N deficiency, and NaCl treatment, whereas the expression of MpMYB02 was down-regulated by NaCl treatment. Our results suggest that the regulatory framework of phenolic metabolism by R2R3-MYB was already established in early land plants.

Membrane trafficking functions of the ANTH/ENTH/VHS domain-containing proteins in plants.

Subcellular localization of proteins acting on the endomembrane system is primarily regulated via membrane trafficking. To obtain and maintain the correct protein composition of the plasma membrane and membrane-bound organelles, the loading of selected cargos into transport vesicles is critically regulated at donor compartments by adaptor proteins binding to the donor membrane, the cargo molecules and the coat-protein complexes, including the clathrin coat. The ANTH/ENTH/VHS domain-containing protein superfamily generally comprises a structurally related ENTH, ANTH, or VHS domain in the N-terminal region and a variable C-terminal region, which is thought to act as an adaptor during transport vesicle formation. This protein family is involved in various plant processes, including pollen tube growth, abiotic stress response and development. In this review, we provide an overview of the recent findings on ANTH/ENTH/VHS domain-containing proteins in plants.

The RopGEF KARAPPO Is Essential for the Initiation of Vegetative Reproduction in Marchantia polymorpha.

Many plants can reproduce vegetatively, producing clonal progeny from vegetative cells; however, little is known about the molecular mechanisms underlying this process. Liverwort (Marchantia polymorpha), a basal land plant, propagates asexually via gemmae, which are clonal plantlets formed in gemma cups on the dorsal side of the vegetative thallus [1]. The initial stage of gemma development involves elongation and asymmetric divisions of a specific type of epidermal cell, called a gemma initial, which forms on the floor of the gemma cup [2, 3]. To investigate the regulatory mechanism underlying gemma development, we focused on two allelic mutants in which no gemma initial formed; these mutants were named karappo, meaning "empty." We used whole-genome sequencing of both mutants and molecular genetic analysis to identify the causal gene, KARAPPO (KAR), which encodes a ROP guanine nucleotide exchange factor (RopGEF) carrying a plant-specific ROP nucleotide exchanger (PRONE) catalytic domain. In vitro GEF assays showed that the full-length KAR protein and the PRONE domain have significant GEF activity toward MpROP, the only ROP GTPase in M. polymorpha. Moreover, genetic complementation experiments showed a significant role for the N- and C-terminal variable regions in gemma development. Our investigation demonstrates an essential role for KAR/RopGEF in the initiation of plantlet development from a differentiated cell, which may involve cell-polarity formation and subsequent asymmetric cell division via activation of ROP signaling, implying a similar developmental mechanism in vegetative reproduction of various land plants.