GmNIGT2a/2b-mediated transcriptional cascade buffers high-nitrogen-triggered nodule senescence in soybean.

The transcription factors GmBBX17 and GmSTFs antagonistically regulate shade avoidance in soybean by oppositely modulating GmSRG1 transcription.

High-density planting represents a promising strategy to enhance crop productivity. However, this agronomic practice inevitably triggers shade avoidance responses (SAR), manifested as stem and petiole elongation, suppressed branching, and altered petiole angles. Elucidating the molecular underpinnings of shade avoidance remains imperative for rationalizing planting density strategies in crop production. Here, we report that soybean SHADE-REDUCED GENE 1 (GmSRG1) inhibits the stem and petiole growth both in white light (WL) and low ratio of Red:Far-red light (Low R:FR) conditions in soybean. GmSRG1 likely represents a catalytically inactive homolog of xyloglucan endotransglucosylase/hydrolase (XTH) that lacks the conserved active site. Despite its enzymatic deficiency, it is associated with enhanced xyloglucan-degrading activity and prevents xyloglucan accumulation in soybean. GmBBX17 binds to the GmSRG1 promoter to repress its transcription, whereas GmSTFs (GmSTF1 and GmSTF2) transcriptionally activate GmSRG1. GmBBX17 physically interacts with GmSTFs to antagonistically regulate GmSRG1 expression. Unlike GmSRG1, its close homolog GmXTH23 is associated with increased xyloglucan accumulation and reduced xyloglucan-degrading activity, while GmSRG1 physically interacts with GmXTH23 and counteracts this GmXTH23-associated effect. Our work reveals an integrated regulatory network comprising the GmBBX17-GmSTFs transcriptional module and the GmSRG1-GmXTH23 regulatory module, which collectively govern shade avoidance architecture in soybean.

LBD-type transcription factors suppress local and systemic nitrogen responses through distinct regulatory pathways

Nitrogen (N) is a major determinant of plant growth and productivity. Because soil N availability and internal N demand fluctuate, plants have evolved sophisticated mechanisms to coordinate N acquisition and utilization at the whole-plant level. However, how this coordination is achieved remains poorly understood. Here, we show that N-inducible LATERAL ORGAN BOUNDARIES DOMAIN transcription factors LBD37, LBD38, and LBD39 (LBDs) function as repressors of local N uptake and assimilation and systemic N-demand signaling in Arabidopsis. Triple mutants lacking these three LBDs displayed enhanced nitrate influx and increased accumulation of nitrate, amino acids, and total N. Transcriptome analysis identified an array of N-starvation- and nitrate-inducible genes derepressed in shoots and roots, including C-TERMINALLY ENCODED PEPTIDE (CEP) and CEP DOWNSTREAM (CEPD) genes, as well as genes involved in N uptake and assimilation. Grafting and genetic analyses revealed that LBDs gate the systemic N-demand signaling relay by repressing CEP and CEPD expression organ-autonomously. We also found that LBDs locally repress genes involved in N uptake and assimilation through a distinct regulatory mechanism. We propose that LBDs are key transcriptional repressors in a regulatory framework for optimizing N acquisition and utilization under fluctuating N conditions at the whole-plant level.

The H3K27me3 reader GmLHP1 impairs Phytophthora sojae resistance by repressing ethylene precursor accumulation in soybean.

Phytophthora root rot, caused by Phytophthora sojae, is a devastating soilborne disease of soybean (Glycine max). However, the epigenetic regulation of soybean responses to P. sojae remains incompletely understood. Here, using genetic, molecular and biochemical approaches, we characterized the functions of LIKE HETEROCHROMATIN PROTEIN 1 (GmLHP1) and its downstream regulatory network. We demonstrated that GmLHP1, as a reader of H3K27me3, negatively regulates soybean resistance to P. sojae. GmLHP1 binds to H3K27me3 peptides in vitro and colocalizes with H3K27me3 marks genome-wide in vivo. The integrated chromatin immunoprecipitation sequencing and RNA sequencing analysis identified the ethylene biosynthesis pathway gene 1-AMINO-CYCLOPROPANE-1-CARBOXYLATE SYNTHASE 18 (GmACS18) as being enriched for H3K27me3 and bound by GmLHP1, leading to its transcriptional downregulation. Notably, GmLHP1 associates with the GmACS18 promoter by directly binding to AATTAA motifs and recognizing H3K27me3 marks. Moreover, GmACS18 enhances defense against P. sojae by accumulating the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Further analysis unveiled that recognition of H3K27me3 by GmLHP1 is essential for regulating soybean resistance to P. sojae through repressing GmACS18 transcription and decreasing ACC accumulation. Our findings reveal a novel epigenetic regulatory mechanism in which the H3K27me3 reader GmLHP1 blocks soybean resistance to P. sojae by repressing ethylene precursor ACC accumulation.

NtGCN2 is associated with multilayer cadmium tolerance in tobacco via coordinated transcriptional changes in growth, antioxidant, and detoxification pathways

OsHMGB1 functions as a transcriptional repressor of OsNRT2.2 in rice: Calcium-regulation and additive function with OsCCA1.

Plant nitrogen uptake and utilization are governed by a complex network involving nitrate transporters and signal-responsive genes. Here, we show that the high mobility group box 1 protein OsHMGB1 directly binds to the OsNRT2.2 promoter and functions as a transcriptional repressor, negatively regulating its expression. Knockout of OsHMGB1 upregulates OsNRT2.2 expression, leading to increased nitrate accumulation and enhanced tolerance to low-nitrogen (LN) conditions in rice seedlings. Furthermore, OsHMGB1 expression is significantly reduced in OsCBL1-knockdown (OsCBL1-KD) plants, suggesting its dependence on OsCBL1-mediated signaling. OsHMGB1 acts additively with OsCCA1, a known repressor that binds the OsNRT2.2 promoter, to negatively regulate OsNRT2.2 expression. Notably, sequence variation in the OsHMGB1 promoter between indica and japonica rice varieties correlates with lower expression levels in indica varieties, which are associated with higher nitrogen use efficiency (NUE)-related agronomic traits, specifically, greater grain yield and increased number of effective panicles, in indica varieties compared with japonica. Together, these findings identify OsHMGB1 as a key repressor of OsNRT2.2, associated with OsCBL1-dependent nitrate signaling and act additively with OsCCA1 to enhance LN tolerance, suggesting that OsHMGB1 expression levels correlate with NUE-related traits under LN conditions. This work elucidates a link between calcium signaling and nitrate response in rice.

GmERF109 Positively Enhances Soybean Resistance to Phytophthora sojae by Transcriptionally Activating GmG4DT‐Like to Promote Glyceollin I Accumulation

ABSTRACT Phytophthora root rot, a devastating disease caused by Phytophthora sojae, poses a significant threat to worldwide soybean ( Glycine max ) production. Therefore, enhancing crop resistance to this pathogen is a major breeding objective. However, the signalling mechanisms underlying the response of soybean plants to P. sojae infection, and the networks and targets of key transcription factors TFs, are not yet fully understood. Here, we reveal the mechanisms and function of GmERF109, which differs in expression between soybean cultivars resistant and susceptible to P. sojae race 1 and encodes an AP2/ERF transcription factor. Molecular evaluation and disease resistance analysis show that GmERF109 is a nucleus‐localized transcription factor that positively regulates soybean resistance to P. sojae. We also demonstrate that GmERF109 targets and activates the expression of GmG4DT‐like, a gene whose role in the biosynthesis of the phytoalexin glyceollin was confirmed through overexpression and RNA interference (RNAi) analyses. GmG4DT‐like also enhances P. sojae resistance. GmG4DT‐like and GmERF109 greatly increased the content of the glyceollin I isomer. Overall, our results suggest that GmERF109 enhances glyceollin accumulation by positively regulating the expression of its target gene GmG4DT‐like, thereby improving soybean resistance to P. sojae. These findings provide novel insights into soybean resistance to Phytophthora root rot and will be useful in efforts to create resistant soybean cultivars.