Dwarf and Increased Branching 1 controls plant height and axillary bud outgrowth in Medicago truncatula

Abstract

Optimizing plant architecture is an efficient approach for breeders to increase crop yields, and phytohormones such as gibberellins (GAs) play an important role in controlling growth. Medicago truncatula is a model legume species, but the molecular mechanisms underlying its architecture are largely unknown. In this study, we examined a tobacco retrotransposon Tnt1-tagged mutant collection of M. truncatula and identified dwarf and increased branching 1 (dib1), which exhibited extreme dwarfism and increased numbers of lateral branches. By analysis of the flanking sequences of Tnt1 insertions in different alleles of the tagged lines, we were able to clone DIB1. Linkage analysis and reverse screening of the flanking-sequence tags identified Medtr2g102570 as the gene corresponding to the DIB1 locus in the dib1 loss-of-function mutants. Phylogenetic analysis indicated that DIB1 was the ortholog of PsGA3ox1/Le in Pisum sativum. Expression analysis using a GUS-staining reporter line showed that DIB1 was expressed in the root apex, pods, and immature seeds. Endogenous GA4 concentrations were markedly decreased whilst some of representative GA biosynthetic enzymes were up-regulated in the dib1 mutant. In addition, exogenous application of GA3 rescued the dib1 mutant phenotypes. Overall, our results suggest that DIB1 controls plant height and axillary bud outgrowth via an influence on the biosynthesis of bioactive GAs. DIB1 could therefore be a good candidate gene for breeders to optimize plant architecture for crop improvement.

From genes to networks: The genetic control of leaf development

“…Similarity, in M. truncatula , loss of DWARF AND INCREASED BRANCHING 1 ( DIB1 ) (syn. MtGA3OX1 ) function also leads plants to produce small leaves due to decreased cell length, whereas plants over‐expressing MtGA20ox1 produce larger leaves, implying the mechanism by which GA regulates leaf size is conserved among different species (Wang et al, 2020; Zhang et al, 2020a). Meanwhile, BR promotes leaf growth via its positive effect on both cell proliferation and cell expansion.…”

The GA 20-Oxidase Encoding Gene MSD1 Controls the Main Stem Elongation in Medicago truncatula

“…Impaired GA biosynthesis caused by defects in early-step genes, CPS , KS , and KO , leads to typical GA-deficient mutant phenotypes, including severe dwarfism with greatly impaired fertility ( Sun and Kamiya, 1994 ; Helliwell et al, 1998 ; Ueguchi-Tanaka et al, 2007 ; Yamaguchi, 2008 ; Chen et al, 2014 ; Regnault et al, 2014 ; Guo et al, 2020 ). By contrast, mutation of late-step genes of GA biosynthesis leads to semi-dwarf phenotypes because of the functional redundancy of homologous genes, such as genes coding for GA3ox in Arabidopsis, rice ( Oryza sativa ), Medicago truncatula and alfalfa ( Medicago sativa ) ( Itoh et al, 2001 ; Dalmadi et al, 2008 ; Hu et al, 2008 ; Zhang et al, 2020 ). Notably, the semi-dwarf “green revolution” phenotype in rice resulted from a mutation in the sd1 gene, which encodes a GA 20-oxidase ( OsGA20ox2 ) ( Sasaki et al, 2002 ; Spielmeyer et al, 2002 ).…”

“…Legumes are second only to grasses in terms of economic and nutritional values, and are the major sources of plant proteins and oils for humans and animals ( Graham and Vance, 2003 ). Studies on several dwarf mutants in pea ( Pisum sativum ), soybean ( Glycine max ), and the model legume M. truncatula have suggested that the GA pathway plays a conserved role in controlling plant height in legumes ( Yaxley et al, 2001 ; Li et al, 2018 ; Guo et al, 2020 ; Zhang et al, 2020 ). Notably, despite the M. truncatula GA20ox family genes exhibited functional redundancy ( Ma et al, 2019 ), overexpression of GA20ox can increase M. truncatula plant height and biomass ( Wang et al, 2020 ), suggesting an application potential of the GA20ox family genes for biomass improvement in legumes.…”

The Genetic Control of the Compound Leaf Patterning in Medicago truncatula

“…Gibberellin (GA) is involved in various processes of plant growth and development, including leaf expansion, seed germination, induction of flowering, and stem elongation. In M. truncatula , Dwarf and Increased Branching 1 ( DIB1 )/ SMALL AND SERRATED LEAF ( SSL ) encodes a gibberellin 3β-hydroxylase (GA3ox) enzyme, catalyzing the final step of the biosynthetic pathway for bioactive GAs ( Zhang et al, 2020 ; Wen et al, 2021 ). The mutant exhibits extreme dwarfism and an increased number of lateral branches, and besides, leaves of the mutant were extremely reduced in all organ sizes and bore a more pronounced leaf margin.…”