Opposing influences of TAC1 and LAZY1 on lateral shoot orientation in Arabidopsis

Authors: HOLLENDER, COURTNEY - Michigan State University; HILL, JOSEPH - Michigan State University; Waite, Jessica; Dardick, Christopher - Chris

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2020
Publication Date: 4/8/2020
Citation: Hollender, C., Hill, J., Waite, J.M., Webb, K.K., Dardick, C.D. 2020. Opposing influences of TAC1 and LAZY1 on lateral shoot orientation in Arabidopsis. Plant Molecular Biology. 10:6051. https://doi.org/10.1038/s41598-020-62962-4.
DOI: https://doi.org/10.1038/s41598-020-62962-4

Interpretive Summary: The labor and other costs associated with management of tree architecture are the most significant expenses to orchardists. We previously discovered two genes with opposing activities, TAC1 and LAZY1, that control the orientation of branches; being vertical or more horizontal. Here, we used the model plant Arabidopsis to study the functional relationships between these two genes. The data supported previous work that LAZY1 is required for plants to sense gravity and showed that TAC1 likely exerts its influence on branch angle by negatively impacting LAZY1 activity.

Technical Abstract: TAC1 and LAZY1 are members of the IGT gene family, which regulates lateral shoot orientation in monocots and dicots. Past research has shown that TAC1 promotes outward orientations and wide branch angles in connection to light perception, while LAZY1 promotes upward shoot growth and shoot bending in response to gravity. Here, we assessed the genetic and functional interactions between these two genes. Both genes were largely expressed in the same tissues during shoot development. Unlike LAZY1 mutants, phenotypic responses of TAC1 mutants in response to gravistimulation did not differ from wild-type, although some transcriptional differences were observed. Arabidopsis homozygous for both TAC1 and LAZY1 exhibited growth and gravity response phenotypes identical to the LAZY1 single mutant, establishing that LAZY1 is epistatic to TAC1. Surprisingly, yeast-two-hybrid screens failed to show direct interactions between TAC1 and LAZY1 proteins, and library screens did not identify any interacting proteins in common. In addition, hormone analyses revealed LAZY1 shoots had exceptionally elevated levels of salicylic acid. Lastly, expression profiling of mutant and wild type plants under normal growth conditions and in response to gravistimulation revealed LAZY1 mutants had substantially more differentially expressed genes (DEGs) than TAC1 plants. The DEGs from LAZY1 transcriptomes included genes related to auxin transport and cell walls, consistent with LAZY1’s established connection to gravity response. Collectively, the data presented here provide a foundation for future study of the regulation of lateral shoot orientation and supports a model in which TAC1 is upstream of LAZY1 and may indirectly negatively regulate LAZY1 function.