Strigolactone insensitivity affects the hormonal homeostasis in barley

Abstract

In response to environmental changes, plants continuously make architectural changes in order to optimize their growth and development. The regulation of plant branching, influenced by environmental conditions and affecting hormone balance and gene expression, is crucial for agronomic purposes due to its direct correlation with yield. Strigolactones (SL), the youngest class of phytohormones, function to shape the architecture of plants by inhibiting axillary outgrowth. Barley plants harboring the mutation in the HvDWARF14 (HvD14) gene, which encodes the SL-specific receptor, produce almost twice as many tillers as wild-type (WT) Sebastian plants. Here, through hormone profiling and comparison of transcriptomic and proteomic changes between 2- and 4-week-old plants of WT and hvd14 genotypes, we elucidate a regulatory mechanism that might affect the tillering of SL-insensitive plants. The analysis showed statistically significant increased cytokinin content and decreased auxin and abscisic acid content in 'bushy' hvd14 compared to WT, which aligns with the commonly known actions of these hormones regarding branching regulation. Further, transcriptomic and proteomic analysis revealed a set of differentially expressed genes (DEG) and abundant proteins (DAP), among which 11.6% and 14.6% were associated with phytohormone-related processes, respectively. Bioinformatics analyses then identified a series of potential SL-dependent transcription factors (TF), which may control the differences observed in the hvd14 transcriptome and proteome. Comparison to available Arabidopsis thaliana data implicates a sub-selection of these TF as being involved in the transduction of SL signal in both monocotyledonous and dicotyledonous plants.

Keywords: Hordeum vulgare; Branching; Phytohormone cross-talk; Strigolactones.

Fig. 1

The phenotype of hvd14. Shoot architecture of (A) 2- and (B) 4-week-old Sebastian and hvd14. (C) Differences in tillers number between WT and mutant plants across 4 months of development. The means ± SE are presented. Asterisks indicate statistically significant differences between genotypes in each time point, as determined by Student’s t-test (p-values corresponding *p < 0.05; **p < 0.01; ***p < 0.001).

Fig. 2

Mutation in HvD14 alters phytohormone content in barley. Measurement of (A) ABA, (B) IAA, (C) CK, (D) GA8, (E) JA, (F) SA content of 2- and 4-week-old Sebastian and hvd14 plants. Asterisks indicate statistically significant differences between samples in Student’s t-test (p-values corresponding *p < 0.05; **p < 0.01; ***p < 0.001). (G) Changes in the hormonal profiles of WT and the mutant during the early stages of plant development. The red and green arrows represent an increase or decrease in hormone content, respectively, with their size indicating the magnitude of the change. An equal sign denotes no change in the level of the analyzed hormone.

Fig. 3

Transcriptome and proteome changes affected by SL-insensitivity. (A) The numbers of differentially expressed genes (DEG) and differentially abundant proteins (DAP) identified after the comparison analysis between 2- and 4-week-old Sebastian and hvd14 plants. The table shows the numbers of DEG and DAP involved in phytohormone-related processes. (B) Pie charts showing distribution of hormone-related DEG and DAP of younger and older hvd14. Venn diagram shows the numbers of specific and shared hormone-related DEG and DAP (duplicates removed) for 2- and 4-week-old hvd14 plants. The illustration was created using BioRender (www.biorender.com).

Fig. 4

TF with over-represented targets in SL-responsive genes of barley and Arabidopsis. Venn diagram showing numbers of identified SL-responsive TF specific for 2- and 4-week old WT vs. hvd14 and Arabidopsis SL-responsive genes selected by Wang et al. 2020. The illustration was created using BioRender (www.biorender.com).

Fig. 5

TF with over-represented targets in SL-responsive genes common for barley and Arabidopsis. Pink boxes indicate TF that target genes associated with phytohormonal processes. The illustration was created using BioRender (www.biorender.com).

Fig. 6

Mutation in HvD14 gene affects the shoot phenotype of barley due to altered hormone homeostasis and altered TF action. Mutation in HvD14 gene leads to the loss of SL-molecule binding properties affecting the plants phenotype. Enhanced axillary growth of hvd14 is connected with altered content of AUX, CK and ABA, as well as changes in TF activity. The illustration was created using BioRender (www.biorender.com).