AUTHOR=Liu Yang , Wang Weiling , Yang Bing , Currey Christopher , Fei Shui-zhang 

TITLE=Functional Analysis of the teosinte branched 1 Gene in the Tetraploid Switchgrass (Panicum virgatum L.) by CRISPR/Cas9-Directed Mutagenesis

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.572193

DOI=10.3389/fpls.2020.572193

ISSN=1664-462X

ABSTRACT=<p>Tillering is an important biomass yield component trait in switchgrass (<italic>Panicum virgatum L</italic>.). <italic>Teosinte branched 1</italic> (<italic>tb1</italic>)/<italic>Branched 1</italic> (<italic>BRC1</italic>) gene is a known regulator for tillering/branching in several plant species; however, its role on tillering in switchgrass remains unknown. Here, we report physiological and molecular characterization of mutants created by CRISPR/Cas9. We successfully obtained nonchimeric <italic>Pvtb1a</italic> and <italic>Pvtb1b</italic> mutants from chimeric T0 mutants using nodal culture. The biallelic <italic>Pvtb1a-Pvtb1b</italic> mutant plants produced significantly more tillers and higher fresh weight biomass than the wild-type plants. The increased tiller number in the mutant plants resulted primarily from hastened outgrowth of lower axillary buds. Increased tillers were also observed in transgene-free BC1 monoallelic mutants for either <italic>Pvtb1a-Pvtb1b</italic> or <italic>Pvtb1b</italic> gene alone, suggesting <italic>Pvtb1</italic> genes act in a dosage-dependent manner. Transcriptome analysis showed 831 genes were differentially expressed in the <italic>Pvtb1</italic>a-<italic>Pvtb1b</italic> double knockdown mutant. Gene Ontology analysis revealed downregulation of <italic>Pvtb1</italic> genes affected multiple biological processes, including transcription, flower development, cell differentiation, and stress/defense responses in edited plants. This study demonstrates that <italic>Pvtb1</italic> genes play a pivotal role in tiller production as a negative regulator in switchgrass and provides opportunities for further research aiming to elucidate the molecular pathway regulating tillering in switchgrass.</p>