Zero-valent iron (nZVI) nanoparticles mediate SlERF1 expression to enhance cadmium stress tolerance in tomato.

Cadmium (Cd) pollution threatens plant physiological and biochemical activities and crop production. Significant progress has been made in characterizing how nanoparticles affect Cd stress tolerance; however, the molecular mechanism of nZVI nanoparticles in Cd stress remains largely uncharacterized. Plants treated with nZVI and exposed to Cd had increased antioxidant capacity and reduced Cd accumulation in plant tissues. The nZVI treatment differentially affected the expression of genes involved in plant environmental responses, including those associated with the ERF transcription factor. SlEFR1 was upregulated by Cd stress in nZVI-treated plants when compared with the control and the predicted protein-protein interactions suggested SlERF1 interacts with proteins associated with plant hormone signaling pathway and related to stress. Yeast overexpressing SlEFR1 grew faster after Cd exposure and significantly had higher Cd stress tolerance when compared with empty vector controls. These results suggest that nZVI induces Cd stress tolerance by activating SlERF1 expression to improve plant growth and nutrient accumulation. Our study reveals the molecular mechanism of Cd stress tolerance for improved plant growth and will support new research on overcoming Cd stress and improving vegetable crop production.

Role of BraRGL1 in regulation of Brassica rapa bolting and flowering.

Gibberellin (GA) plays a major role in controlling Brassica rapa stalk development. As an essential negative regulator of GA signal transduction, DELLA proteins may exert significant effects on stalk development. However, the regulatory mechanisms underlying this regulation remain unclear. In this study, we report highly efficient and inheritable mutagenesis using the CRISPR/Cas9 gene editing system in BraPDS (phytoene desaturase) and BraRGL1 (key DELLA protein) genes. We observed a loss-of-function mutation in BraRGL1 due to two amino acids in GRAS domain. The flower bud differentiation and bolting time of BraRGL1 mutants were significantly advanced. The expression of GA-regulatory protein (BraGASA6), flowering related genes (BraSOC1, BraLFY), expansion protein (BraEXPA11) and xyloglucan endotransferase (BraXTH3) genes was also significantly upregulated in these mutants. BraRGL1-overexpressing plants displayed the contrasting phenotypes. BraRGL1 mutants were more sensitive to GA signaling. BraRGL1 interacted with BraSOC1, and the interaction intensity decreased after GA3 treatment. In addition, BraRGL1 inhibited the transcription-activation ability of BraSOC1 for BraXTH3 and BraLFY genes, but the presence of GA3 enhanced the activation ability of BraSOC1, suggesting that the BraRGL1-BraSOC1 module regulates bolting and flowering of B. rapa through GA signal transduction. Thus, we hypothesized that BraRGL1 is degraded, and BraSOC1 is released in the presence of GA3, which promotes the expression of BraXTH3 and BraLFY, thereby inducing stalk development in B. rapa. Further, the BraRGL1-M mutant promoted the flower bud differentiation without affecting the stalk quality. Thus, BraRGL1 can serve as a valuable target for the molecular breeding of early maturing varieties.

Genome-wide identification of BcGRF genes in flowering Chinese cabbage and preliminary functional analysis of BcGRF8 in nitrogen metabolism.

Growth-regulating factors (GRFs) are a unique family of transcription factors with well-characterized functions in plant growth and development. However, few studies have evaluated their roles in the absorption and assimilation of nitrate. In this study, we characterized the GRF family genes of flowering Chinese cabbage (Brassica campestris), an important vegetable crop in South China. Using bioinformatics methods, we identified BcGRF genes and analyzed their evolutionary relationships, conserved motifs, and sequence characteristics. Through genome-wide analysis, we identified 17 BcGRF genes distributed on seven chromosomes. A phylogenetic analysis revealed that the BcGRF genes could be categorized into five subfamilies. RT-qPCR analysis showed that BcGRF1, 8, 10, and 17 expression clearly increased in response to nitrogen (N) deficiency, particularly at 8 h after treatment. BcGRF8 expression was the most sensitive to N deficiency and was significantly correlated with the expression patterns of most key genes related to N metabolism. Using yeast one-hybrid and dual-luciferase assays, we discovered that BcGRF8 strongly enhances the driving activity of the BcNRT1.1 gene promoter. Next, we investigated the molecular mechanism by which BcGRF8 participates in nitrate assimilation and N signaling pathways by expressing it in Arabidopsis. BcGRF8 was localized in the cell nucleus and BcGRF8 overexpression significantly increased the shoot and root fresh weights, seedling root length, and lateral root number in Arabidopsis. In addition, BcGRF8 overexpression considerably reduced the nitrate contents under both nitrate-poor and -rich conditions in Arabidopsis. Finally, we found that BcGRF8 broadly regulates genes related to N uptake, utilization, and signaling. Our results demonstrate that BcGRF8 substantially accelerates plant growth and nitrate assimilation under both nitrate-poor and -rich conditions by increasing the number of lateral roots and the expression of genes involved in N uptake and assimilation, providing a basis for crop improvement.

BcGRP23: A novel gene involved in the chlorophyll metabolic pathway that is activated by BES1 in flowering Chinese cabbage.

Glycine-rich proteins (GRPs) are a large family of proteins that play vital roles in cell wall remodeling, metabolism and development, and abiotic stress response. Although the functions of GRPs in cell wall remodeling have been extensively characterized, only a few studies have explored their effects on chlorophyll metabolism and hormone response. Accordingly, we aimed to determine the molecular mechanism of BcGRP23 and its role in chlorophyll metabolism and the BRI1-EMS-SUPPRESSOR 1 (BES1) signaling pathway in flowering Chinese cabbage. The expression levels of BcGRP23 in the leaves and stems gradually decreased with increasing growth and development of flowering Chinese cabbage, while BcGRP23 was barely expressed after flowering. As plant growth continued, the GUS (ß-glucuronidase) stain gradually became lighter in hypocotyls and was largely free of growth points. The petioles and stems of BcGRP23-silenced plants lost their green color, and the contents of chlorophyll a (Chl a) and Chl b were significantly reduced. Further research revealed that the expression levels of chlorophyll degradation-related genes were significantly increased in silenced plants compared with the control; however, the opposite was noted for the BcGRP23-overexpressing lines. The BcGRP23 promoter sequence contains numerous hormone-responsive elements. In fact, the expression of BcGRP23 was upregulated in flowering Chinese cabbage following treatment with the hormones indole-3-acetic acid (IAA), gibberellin (GA), 6-benzylaminopurine (6-BA), methyl jasmonate (MeJA), and brassinosteroid (BR). Treatment with BR led to the most significant upregulation. BES1, in response to BRs, directly activated the BcGRP23 promoter. Overall, BcGRP23 regulated the expression of chlorophyll degradation-related genes, thereby affecting the chlorophyll content. Furthermore, the expression of BcGRP23 was significantly regulated by exogenous BR application and was directly activated by BES1. These findings preliminarily suggest the molecular mechanism and regulatory pathway of BcGRP23 in the growth and development of flowering Chinese cabbage plants and their response to environmental stress.