Transcriptome analysis suggests cytokinin and gibberellin signaling may account for differences between spring and winter canola (B. napus) root development

Authors: ARIFUZZAMAN, MUHAMMAD - North Dakota State University; Horvath, David; RAHMAN, MUKHLESUR - North Dakota State University

Submitted to: Journal of Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2020
Publication Date: 8/4/2020
Citation: Arifuzzaman, M., Horvath, D.P., Rahman, M. 2020. Transcriptome analysis suggests cytokinin and gibberellin signaling may account for differences between spring and winter canola (B. napus) root development. Journal of Plant Biology. https://doi.org/10.1007/s12374-020-09270-6.
DOI: https://doi.org/10.1007/s12374-020-09270-6

Interpretive Summary: Winter canola produces larger root systems than spring canola. Larger root systems are associated with higher yield, and thus, the genes and signals controlling root growth are of interest to breeders. Here, we looked to see what genes were turned on and off during two different time points (30 days and 60 days after germination) in the roots of winter and spring canola. The genes we found to be up and down regulated provide clues that implicate a role for cytokinin and gibberellic acid as being the key regulators that cause the differences between winter and spring root growth habits. This information will help breeders target genes controlling the accumulation of these two growth-regulators, and should eventually allow the breeding of spring canola with more robust root systems.

Technical Abstract: Background: Spring and winter canola growth habits are different from each other in terms of yield and plant morphology. Spring type canola produces significantly smaller and less vigorous roots compared to winter type canola at the same growing stage. We conducted this experiment to identify the gene regulatory networks and cross talk among phytohormones and genetic variation that may responsible for the difference between the root system of the two growth types. Results: We analyzed transcriptomes from the root samples collected from two spring and two winter type canola at two time points, 30 and 60 days. A total of 169,646 transcripts were analyzed. Among them, 582 and 555 transcripts were found to be significantly differentially expressed between spring and winter types at 30 and 60 days, respectively. Several auxin responsive family genes were significantly differentially expressed between spring and winter types at both time points but no distinct pattern of differential regulation among auxin response or signaling genes was observed in either of the growth types. This would be most consistent with the hypothesis that some other non-auxin mediated root growth regulation might be responsible for the root system differences between the two types. Type-A and type-B ARABIDOPSIS RESPONSE REGULATOR (ARR) genes and gene sets involved in cytokinin signaling pathway were up-regulated in spring type at 60 days. This would be consistent with higher cytokinin activity in spring type root system at later growth stage which has proven to inhibit root growth. In addition, several gibberellin responsive and gibberellin signaling gene sets were also upregulated in spring type at 60 days compared to….. We observed an elongated root system with fewer root branches in spring type at 60 day compared to winter type at 60 day in this study. Root elongation but inhibited lateral root formation is in consistent with a role for gibberellin in promoting the spring type root architecture. Conclusion: Cytokinin and gibberellin may play a major role in reduced root growth in spring canola although gibberellin may promote the tap root elongation in the spring canola. Extensive gene expression data generated in this research will further assist to understand the natural variation of root system in canola growth habits.