Characterization of a barley ( L.) mutant with multiple stem nodes and spikes and dwarf () and fine-mapping of its causal gene.

Introduction: Multiple nodes and dwarf mutants in barley are a valuable resource for identifying genes that control shoot branching, vegetative growth and development.

Methods: In this study, physiological, microscopic and genetic analysis were conducted to characterize and fine-map the underling gene of a barley mutant with Multiple Stem Nodes and Spikes and Dwarf (), which was selected from EMS- and Co-treated barley . Edamai 934.

Results And Discussion: The mutant had more stem nodes, lower plant height and a shorter plastochron than Edamai 934. Moreover, the mutant had two or more spikes on each tiller. Microscopic analysis showed that the dwarf phenotype of resulted from reduced cell lengths and cell numbers in the stem. Further physiological analysis showed that was GA-deficient, with its plant height increasing after external GA application. Genetic analysis revealed that a single recessive nuclear gene, namely, Hv, controlled the phenotype. Using a segregating population derived from Harrington and the mutant, Hv was fine-mapped on chromosome 5H in a 200 kb interval using bulked segregant analysis (BSA) coupled with RNA-sequencing (BSR-seq), with a C-T substitution in the exon of HvTCP25 co-segregating with the phenotype. RNA-seq analysis showed that a gene encoding gibberellin 2-oxidase 8, a negative regulator of GA biosynthesis, was upregulated in the mutant. Several known genes related to inflorescence development that were also upregulated and enriched in the mutant. Collectively, we propose that Hv regulates the plastochron and morphology of reproductive organs, likely by coordinating GA homeostasis and changed expression of floral development related genes in barley. This study offers valuable insights into the molecular regulation of barley plant architecture and inflorescence development.