Gutsche, N. | Search bioRxiv

bioRxiv2023

Identification and characterization of DICER-LIKE genes and their roles in Marchantia polymorpha development and stress adaptation

DICER-LIKE (DCL) proteins have a central role in plant small RNA (sRNA) biogenesis. The Marchantia polymorpha genome encodes four DCL proteins: two DCL1 homologs, MpDCL1a and MpDCL1b, MpDCL3 and MpDCL4. While MpDCL1a, MpDCL3 and MpDCL4 show high similarities to their orthologs in Physcomitrium patens and Arabidopsis thaliana, MpDCL1b shares only a limited homology with PpDCL1b, but it is very similar, in terms of functional domains, to orthologs in Anthoceros agrestis and Salvinia cucullata. We generated Mpdclge mutant lines via the CRISPR/Cas9 system and performed comprehensive phenotypic analyses of these mutant lines, under control and salt stress conditions as well as upon exogenous naphthaleneacetic acid (NAA) and abscisic acid (ABA) treatments to gain insights into the respective MpDCL functions. While Mpdcl1age mutants display severe developmental aberrations throughout their development, no adverse phenotypic changes are detectable in Mpdcl1bge and Mpdcl4ge mutants except the development of less and smaller male sexual organs (antheridiophores) when they are cultivated under photoperiod conditions supplemented with far-red light. Mpdcl3ge mutants display rosette-shaped thallus formation and overall faster development, but are not able to form antheridiophores. The rosette-shaped thallus development of Mpdcl3ge can be reverted to a wild-type-like thallus growth upon NAA treatment. Mpdcl1bge mutants can tolerate high levels of salt, whereas Mpdcl4ge mutants show higher salt sensitivity. Moreover, Mpdcl1age and Mpdcl3ge mutants show an ABA-hypersensitive phenotype. It can be concluded that the observed phenotypic alterations, under normal or treatment conditions, are linked to the mutations in the respective MpDCLs and hence to defective or altered sRNA biogenesis pathways in M. polymorpha. In conclusion, MpDCLs and their associated sRNAs regulate development, abiotic stress and phytohormonal response in M. polymorpha.

plant biology↗

bioRxiv2022

Contrasting and conserved roles of NPR proteins in diverged land plant lineages

The NPR proteins function as salicylic acid (SA) receptors in Arabidopsis thaliana. AtNPR1 plays a central role in SA-induced transcriptional reprogramming whereby positively regulates SA-mediated defense. NPRs are found in the genomes of nearly all land plants. However, we know little about the molecular functions and physiological roles of NPRs in most plant species. Our phylogenetic and alignment analyses show that Brassicaceae NPR1-like proteins have characteristically gained or lost functional residues or motifs identified in AtNPRs, pointing to the possibility of a unique evolutionary trajectory for the Brassicaceae NPR1-like proteins that has resulted in peculiar functions. In line with this observation, we find that the only NPR in Marchantia polymorpha, MpNPR, is not the master regulator of SA-induced transcriptional reprogramming and negatively regulates bacterial resistance in this species. Interspecies complementation analysis indicated that the molecular properties of AtNPR1 and MpNPR are partially conserved, implying the diversification of NPR-associated pathways contributed to distinct roles of NPR in different species. The Mpnpr transcriptome suggested potential roles of MpNPR in heat and far-red light responses. We identify both Mpnpr and Atnpr1-1 display enhanced thermomorphogenesis. NPRs and NPR-associated pathways clearly have evolved distinctively in diverged land plant lineages to cope with different terrestrial environments.

plant biology↗