From liguleless loci to a cell-type resolution map of leaf angle
Leaf angle has long been treated as a polygenic architecture trait. A multi-model GWAS of 212 Southeast China inbred lines identified 14 significant SNPs and 342 candidate genes, with broad-sense heritability above 80% [4], while BSA plus F2 linkage mapping in a C144 x Su54 cross recovered QTL for plant height, tassel branch number and leaf angle [6]. Functional work on liguleless1 showed that recessive lg1 reduces leaf angle, with a 130 bp Tourist MITE insertion in exon 2 truncating the LG1 protein and a 3:1 wide:narrow segregation in F2 populations [8]. Together these studies established that leaf angle is heritable, polygenic and anchored by ligular-region genes, but they could not say which cells execute the trait.
The new atlas supplies that missing cell-type layer. By profiling the B73 ligular region across S1-S3 and integrating published shoot apical meristem and leaf primordium data for S0, the authors assembled 65,691 high-quality nuclei into 32 clusters annotated with markers such as LG1, KN1, SWEET13a/b/c and EXPA1/EXPB8 [1]. This is a methodological advance over earlier bulk and single-stage transcriptomics, because it resolves adaxial versus abaxial hypodermal populations and places known leaf angle regulators into discrete cell contexts [1].
Brassinosteroid does two opposite things in the same organ
The central mechanistic claim is that BR inhibits cell division in the adaxial division zone while promoting elongation in adaxial hypodermal cells, so BR treatment produces ectopic auricle and ligule emergence [1]. This dual action is supported by hormone treatments across a range of concentrations and by histological sections showing BR-induced increases in leaf angle and hypodermal cell length [1]. The interpretation is that BR does not simply 'increase leaf angle'; it re-times a cell fate transition at the blade-sheath boundary.
This fits a broader BR literature while sharpening it. In sugarcane, moderate BR (3-5 uM) promoted cell enlargement and increased leaf angle, whereas higher levels (>=10 uM) reduced cell size and decreased leaf angle [9], and BR application in maize mesocotyls altered sugar metabolism under low temperature [2]. The maize atlas adds cell-type specificity and a developmental stage axis that these physiological studies lacked, but the dose-dependent reversal seen in sugarcane [9] is a reminder that the direction of BR effects depends on concentration and tissue context.
Two sequential modules: GELP2/3/6 for emergence, LG1-BZR1 for expansion
At early stages, GDSL esterases/lipase genes GELP2/3/6 act as regulators of ligular emergence; their disruption causes both ectopic initiation and impaired outgrowth of ligule and auricle [1]. At later stages, LG1 and BZR1 cooperatively drive adaxial hypodermal cell elongation, activating bHLH30 and bHLH155, which in turn promote targets such as EXPA5 [1]. Genetic support includes expa5-1 mutants with reduced leaf angle and plant height, and ChIP-qPCR plus transient assays showing direct binding of LG1 and BZR1 to bHLH30 and bHLH155 promoters [1].
This module structure helps explain why earlier single-gene studies gave partial pictures. lg1 loss-of-function narrows leaf angle [8], and ZmDRL1 knockouts enlarge pulvinus cells and increase leaf angle through hormone-related pathways [5]. The atlas places these genes in a temporal sequence, but it also implies that manipulating one node may shift leaf angle without reproducing the full inbred-line spectrum.
Inbred-line diversity as a two-step elongation-then-lignification program
The most breeding-relevant result is comparative: variation in adaxial cell elongation and subsequent hypodermal lignification explains leaf angle diversity across inbred lines [1]. In 83 inbred lines, BR-specific induced leaf angle increase correlated with tasseling-stage leaf angle, and EXPA5 expression correlated with leaf angle [1]. Compact inbred lines such as Z58 showed adaxial lignification and higher expression of lignin biosynthesis genes including CAD8, C3H7, CCOAOMT2, 4CL2, MYB41, NAC53 and C4H3 compared with flat-type lines [1].
This aligns with independent evidence that mechanical strength is an underrecognized breeding target: lignin deposition in ligular sclerenchyma and adaxial hypodermal cells, mediated by NST2 and NST3, reinforces support and reduces leaf angle across compact, intermediate and expanded inbred types [10]. It also resonates with work showing that auricle cells acquire a distinct fate from blade, sheath and ligule [11]. The convergence across these studies strengthens the interpretation that lignification acts as a maturity checkpoint terminating hormone-driven elongation [1][10].
What the atlas does not yet settle
The mechanism is inferred from specific developmental stages and a limited set of inbred lines under controlled or short-term treatment conditions [1]. Field yield and multi-environment stability were not tested, so the claim that these targets can deliver high-yield, dense-planting ideotypes remains a breeding hypothesis rather than a demonstrated outcome [1]. The BR dose reversal reported in sugarcane [9] and the environmental sensitivity of leaf morphology QTL across locations [7] both caution against assuming that a single hormonal manipulation will translate uniformly.
There is also unresolved genetic architecture. GWAS and QTL studies continue to nominate many small-effect loci for leaf angle [4][6], and heterosis mapping shows that leaf morphological traits differ across heterotic groups and can be influenced by maternal effects [7]. The atlas explains a cellular program, not the full polygenic variance. Whether GELP2/3/6, LG1-BZR1, bHLH30/155 and EXPA5 alleles account for a meaningful share of natural leaf angle variation across diverse germplasm is an open question that requires allele-level and multi-environment validation.
About These Sources
This research page is built on 11 peer-reviewed studies — published from 2025 to 2026, 11 from 2024 or later — selected as the most relevant from 13 studies that passed quality screening, drawn from 55 papers retrieved from a database of over 500 million.
Sources used in this answer
A single-nucleus atlas of ligular region uncovers brassinosteroid-driven cell fate transitions controlling leaf angle in maize
The anchor paper builds a single-nucleus atlas of the maize ligular region and shows that BR-driven cell fate transitions, GELP2/3/6, LG1-BZR1, bHLH30/155 and EXPA5 control leaf angle, with adaxial elongation and lignification explaining inbred-line diversity [1].
Brassinosteroids Enhance Low-Temperature Resistance by Promoting the Formation of Sugars in Maize Mesocotyls
Exogenous EBR application in maize mesocotyls under low temperature promoted soluble sugar accumulation and altered starch, sucrose and glucose relationships, linking BR to sugar metabolism under stress [3].
Molecular dissection and functional characterization of the liguleless1 gene for manipulation of leaf angle in maize
Recessive lg1 significantly reduces maize leaf angle and has become a breeding choice for high plant density, with a 3:1 wide:narrow segregation reported in F2 populations [4].
Multi-model GWAS reveals key loci for leaf angle in maize inbred lines from southeast China.
A multi-model GWAS of 212 Southeast China inbred lines identified 14 significant SNPs and 342 candidate genes for leaf angle, with broad-sense heritability above 80% and KASP markers developed for three stable SNPs [6].
ZmDRL1 regulates maize leaf angle via phytohormone signaling.
ZmDRL1 loss-of-function and CRISPR knockout lines showed increased leaf angle and enlarged pulvinus cells in B73 and Zong31 backgrounds, with transcriptomic and metabolomic evidence implicating IAA, ABA and SA pathways and ARF2 interaction [7].
QTL mapping, validation, and candidate gene predicting for maize plant architecture traits via bulked segregant analysis plus linkage analysis with F₂ population.
BSA plus F2 linkage mapping in a C144 x Su54 cross identified QTL for plant height, tassel branch number and leaf angle, including qLA5-2, and nominated candidate genes for molecular marker-assisted breeding [8].
Quantitative trait loci mapping of heterosis for leaf morphological traits and candidate gene identification in maize.
QTL mapping of heterosis for leaf morphological traits across six testcross populations from three heterotic groups found high heritability, maternal effects on leaf length, and candidate genes including SKP1-like and ALBINO3 [9].
Molecular dissection and functional characterization of the liguleless1 gene for manipulation of leaf angle in maize.
Sequencing of the lg1 gene across seven wild-type and one mutant inbred identified a 130 bp Tourist MITE insertion in exon 2, developed a co-dominant InDel marker, and classified 48 inbreds into 35 haplotypes [10].
Systematic identification and functional insights into IGT family members involved in leaf angle regulation and abiotic stress response in sugarcane.
In sugarcane, moderate BR (3-5 uM) promoted cell enlargement and increased leaf angle while higher levels (>=10 uM) reduced cell size and leaf angle, with IGT genes including ShLAZY1 and ShDRO2 responding to BR [11].
Mechanical Strength: An Unrecognised Target in the Genetic Improvement of Crops.
Mechanical strength analysis across compact, intermediate and expanded maize inbred lines identified adaxial hypodermal lignin deposition and NST2/NST3 as key determinants of leaf angle, framing leaf angle as a dynamic mechanical equilibrium [12].
Cell fate acquisition at a de novo developmental boundary in the maize leaf.
Cell lineage mapping, morphometrics and cell-specific transcriptomics at the maize blade-sheath boundary showed that auricle initial cells are recruited from blade founder cells and acquire a distinct auricle fate [13].