A maize semi-dwarf mutant reveals a GRAS transcription factor involved in brassinosteroid signaling

Authors: KAUR, AMANPREET - Purdue University; Best, Norman; HARTWIG, THOMAS - Heinrich-Heine University; BUDKA, JOSH - Purdue University; KHANGURA, RAJDEEP - Purdue University; MACKENZIE, STEVEN - Purdue University; ARAGÓN-RAYGOZA, ALEJANDRO - North Carolina State University; STRABLE, JOSH - North Carolina State University; SCHULZ, BURKHARD - Purdue University; DILKES, BRIAN - Purdue University

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2024
Publication Date: 5/6/2024
Citation: Kaur, A., Best, N.B., Hartwig, T., Budka, J., Khangura, R., Mackenzie, S., Aragón-Raygoza, A., Strable, J., Schulz, B., Dilkes, B. 2024. A maize semi-dwarf mutant reveals a GRAS transcription factor involved in brassinosteroid signaling. Plant Physiology. Article kiae147. https://doi.org/10.1093/plphys/kiae147.
DOI: https://doi.org/10.1093/plphys/kiae147

Interpretive Summary: Identification and characterization of genes involved in hormone signaling pathways are important to modify plant architecture to increase yield. In this manuscript, we characterize a gene responsible for a maize mutant phenotype with upright leaf angle. Making leaves more upright allows for greater light capture to increase photosynthetic capabilities of the plant and also to further increase planting densities to increase yield. Through transcriptomic and quantitative genetic approaches, we identified that this gene regulates the signaling pathway of a group of essential plant hormone called brassinosteroids. Studying the genetic interaction of this mutant gene with other mutant genes involved in hormone pathways, we identified that this gene not only controls leaf angle, but also helps control reproductive development and branching of shoots and tassels. Modification of this gene and its downstream targets in elite breeding lines could allow breeders to further improve plant architecture to increase yields.

Technical Abstract: Brassinosteroids (BR) and gibberellins (GA) regulate plant height and leaf angle in maize (Zea mays). Mutants with defects in BR or GA biosynthesis or signaling identify components of these pathways and enhance our knowledge about plant growth and development. In this study, we characterized three recessive mutant alleles of GRAS transcription factor 42 (gras42) in maize, a GRAS transcription factor gene orthologous to the DWARF AND LOW TILLERING (DLT) gene of rice (Oryza sativa). These maize mutants exhibited semi-dwarf stature, shorter and wider leaves, and more upright leaf angle. Transcriptome analysis revealed a role for GRAS42 as a determinant of BR signaling. Analysis of the expression consequences from loss of GRAS42 in the gras42-mu1021149 mutant indicated a weak loss of BR signaling in the mutant, consistent with its previously demonstrated role in BR signaling in rice. Loss of BR signaling was also evident by the enhancement of weak BR biosynthetic mutant alleles in double mutants of nana plant1-1 and gras42-mu1021149. The gras42-mu1021149 mutant had little effect on GA-regulated gene expression, suggesting that GRAS42 is not a regulator of core GA signaling genes in maize. Single-cell expression data identified gras42 expressed among cells in the G2/M phase of the cell cycle consistent with its previously demonstrated role in cell cycle gene expression in Arabidopsis (Arabidopsis thaliana). Cis-acting natural variation controlling GRAS42 transcript accumulation was identified by expression genome-wide association study (eGWAS) in maize. Our results demonstrate a conserved role for GRAS42/SCARECROW-LIKE 28 (SCL28)/DLT in BR signaling, clarify the role of this gene in GA signaling, and suggest mechanisms of tillering and leaf angle control by BR.