Transcriptional responses to gibberellin in the maize tassel and control by DELLA domain proteins

Abstract

SUMMARY The plant hormone gibberellin (GA) impacts plant growth and development differently depending on the developmental context. In the maize (Zea mays) tassel, application of GA alters floral development, resulting in the persistence of pistils. GA signaling is achieved by the GA‐dependent turnover of DELLA domain transcription factors, encoded by dwarf8 (d8) and dwarf9 (d9) in maize. The D8‐Mpl and D9‐1 alleles disrupt GA signaling, resulting in short plants and normal tassel floret development in the presence of excess GA. However, D9‐1 mutants are unable to block GA‐induced pistil development. Gene expression in developing tassels of D8‐Mpl and D9‐1 mutants and their wild‐type siblings was determined upon excess GA3 and mock treatments. Using GA‐sensitive transcripts as reporters of GA signaling, we identified a weak loss of repression under mock conditions in both mutants, with the effect in D9‐1 being greater. D9‐1 was also less able to repress GA signaling in the presence of excess GA3. We treated a diverse set of maize inbred lines with excess GA3 and measured the phenotypic consequences on multiple aspects of development (e.g., height and pistil persistence in tassel florets). Genotype affected all GA‐regulated phenotypes but there was no correlation between any of the GA‐affected phenotypes, indicating that the complexity of the relationship between GA and development extends beyond the two‐gene epistasis previously demonstrated for GA and brassinosteroid biosynthetic mutants.

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

“…Some gras42-mu1021149 single mutant tassels exhibited barren branches ( Fig. 10 ) as was observed in GA excess treatments ( Best and Dilkes 2022 ). All gras42-mu1021149/d1 tassels were completely normal demonstrating that d1 suppresses the gras42-mu1021149 barren phenotype and that, just as was the case for the presence of pistils in the tassel for BR-deficient mutants, GA is required for the gras42-mu1021149 tassel phenotype.…”

“…All gras42-mu1021149/d1 tassels were completely normal demonstrating that d1 suppresses the gras42-mu1021149 barren phenotype and that, just as was the case for the presence of pistils in the tassel for BR-deficient mutants, GA is required for the gras42-mu1021149 tassel phenotype. It has been previously shown that GA can induce male sterility in maize ( Nelson and Rossman 1958 ; Best and Dilkes 2022 ). The suppression of the barren phenotype by gras42-mu1021149/d1 double mutants indicates that the male sterility in gras42-mu1021149 may be due to excess GA in this tissue.…”

Factors specifying sex determination in maize

“…Inflorescence phenotype in Dwarf mutants either recessives ( d ) or dominants ( D ) is related to reduction of GA level, and it shows different degrees of a masculinizing phenotype in ears with anther development in ear florets, which produces upper female ear florets with both anthers and pistils, showing bisexual flowers and lower ear florets with androecium identity (Best and Dilkes 2022 ). The phenotype in tassel anthers is mostly like in wild-type plants, with normal anther development but in some cases with compact tassels (Best et al 2016 ).…”