Role of LBD14 during ABA-mediated control of root system architecture in Arabidopsis

Genome-wide identification and analysis of Lateral Organ Boundaries Domain (LBD) transcription factor gene family in melon (Cucumis melo L.)

Background

Lateral Organ Boundaries Domain (LBD) transcription factor (TF) gene family members play very critical roles in several biological processes like plant-spesific development and growth process, tissue regeneration, different biotic and abiotic stress responses in plant tissues and organs. The LBD genes have been analyzed in various species. Melon (Cucumis melo L.), a member of the Cucurbitaceae family, is economically important and contains important molecules for nutrition and human health such as vitamins A and C, β-carotenes, phenolic acids, phenolic acids, minerals and folic acid. However, no studies have been reported so far about LBD genes in melon hence this is the first study for LBD genes in this plant.

Results

In this study, 40 melon CmLBD TF genes were identified, which were separated into seven groups through phylogenetic analysis. Cis-acting elements showed that these genes were associated with plant growth and development, phytohormone and abiotic stress responses. Gene Ontology (GO) analysis revealed that of CmLBD genes especially function in regulation and developmental processes. The in silico and qRT-PCR expression patterns demonstrated that CmLBD01 and CmLBD18 are highly expressed in root and leaf tissues, CmLBD03 and CmLBD14 displayed a high expression in male-female flower and ovary tissues.

Conclusions

These results may provide important contributions for future research on the functional characterization of the melon LBD gene family and the outputs of this study can provide information about the evolution and characteristics of melon LBD gene family for next studies.

ZmLBD5 Increases Drought Sensitivity by Suppressing ROS Accumulation in Arabidopsis

Drought stress is known to significantly limit crop growth and productivity. Lateral organ boundary domain (LBD) transcription factors-particularly class-I members-play essential roles in plant development and biotic stress. However, little information is available on class-II LBD genes related to abiotic stress in maize. Here, we cloned a maize class-II LBD transcription factor, ZmLBD5, and identified its function in drought stress. Transient expression, transactivation, and dimerization assays demonstrated that ZmLBD5 was localized in the nucleus, without transactivation, and could form a homodimer or heterodimer. Promoter analysis demonstrated that multiple drought-stress-related and ABA response cis-acting elements are present in the promoter region of ZmLBD5. Overexpression of ZmLBD5 in Arabidopsis promotes plant growth under normal conditions, and suppresses drought tolerance under drought conditions. Furthermore, the overexpression of ZmLBD5 increased the water loss rate, stomatal number, and stomatal apertures. DAB and NBT staining demonstrated that the reactive oxygen species (ROS) decreased in ZmLBD5-overexpressed Arabidopsis. A physiological index assay also revealed that SOD and POD activities in ZmLBD5-overexpressed Arabidopsis were higher than those in wild-type Arabidopsis. These results revealed the role of ZmLBD5 in drought stress by regulating ROS levels.

Genome-Wide Identification and Expression Analysis of LBD Transcription Factor Genes in Passion Fruit (Passiflora edulis)

The lateral organ boundary domain (LBD) gene is a plant-specific transcription factor that plays a crucial role in plant growth and development, including the development of lateral vegetative organs such as leaf and root development, as well as floral organs such as sepal, petal, and pollen development. Passion fruit is a tropical fruit with important agricultural, economic and ornamental value. However, there is no systematic research report available on the LBD gene family of passion fruit. In this study, a genome-wide analysis of passion fruit LBD genes identified 33 PeLBDs that were unevenly distributed across nine chromosomes. According to phylogenetic and gene structure analysis, PeLBDs were divided into two categories: Class I (27) and Class II (6). Homologous protein modeling results showed that the gene members of the two subfamilies were structurally and functionally similar. Cis-acting element and target gene prediction analysis suggested that PeLBDs might participate in various biological processes by regulating diverse target genes involved in growth and development, metabolism, hormones and stress response. Collinearity analysis indicated that the expansion of the PeLBD gene family likely took place mainly by segmental duplication, and some duplicated gene pairs such as PeLBD13/15 might show functional redundancy, while most duplicated gene pairs such as PeLBD8/12 showed different expression profiles indicating their functional diversification. After filtering low expressed genes, all Class Id PeLBDs were more highly expressed during pollen development. At the same, all Class Ic and many other PeLBDs were relatively highly expressed during ovule development, similar with their homologous LBD genes in Arabidopsis, indicating their potential regulatory roles in reproductive tissue development in passion fruit. PeLBDs that were highly expressed in floral tissues were also expressed at a higher level in tendrils with some differences, indicating the close relationships of tendrils to floral tissues. Some genes such as PeLBD23/25 might be simultaneously related to floral development and leaf early formation in passion fruit, while other PeLBDs showed a strong tissue-specific expression. For example, PeLBD17/27/29 were specifically expressed in floral tissues, while PeLBD11 were only highly expressed in fruit, suggesting their specific function in the development of certain tissues. A qRT-PCR was conducted to verify the expression levels of six PeLBDs in different tissues. Our analysis provides a basis for the functional analysis of LBD genes and new insights into their regulatory roles in floral and vegetative tissue development.

Phylogeny and Functions of LOB Domain Proteins in Plants

Lateral organ boundaries (LOB) domain (LBD) genes, a gene family encoding plant-specific transcription factors, play important roles in plant growth and development. At present, though there have been a number of genome-wide analyses on LBD gene families and functional studies on individual LBD proteins, the diverse functions of LBD family members still confuse researchers and an effective strategy is required to summarize their functional diversity. To further integrate and improve our understanding of the phylogenetic classification, functional characteristics and regulatory mechanisms of LBD proteins, we review and discuss the functional characteristics of LBD proteins according to their classifications under a phylogenetic framework. It is proved that this strategy is effective in the anatomy of diverse functions of LBD family members. Additionally, by phylogenetic analysis, one monocot-specific and one eudicot-specific subclade of LBD proteins were found and their biological significance in monocot and eudicot development were also discussed separately. The review will help us better understand the functional diversity of LBD proteins and facilitate further studies on this plant-specific transcription factor family.

LBD13 positively regulates lateral root formation in Arabidopsis

Lateral Organ Boundaries Domain 13 (LBD13), which is expressed in emerged lateral roots and encodes a transcriptional activator, plays an important role in lateral root formation in Arabidopsis. Lateral roots (LRs) are major determinants of root system architecture, contributing to the survival strategies of plants. Members of the LBD gene family encode plant-specific transcription factors that play key roles in plant organ development. Several LBD genes, such as LBD14, 16, 18, 29, and 33, have been shown to play important roles in regulating LR development in Arabidopsis. In the present study, we show that LBD13 is expressed in emerged LRs and LR meristems of elongated LRs and regulates LR formation in Arabidopsis. Transient gene expression assays with Arabidopsis protoplasts showed that LBD13 is localized to the nucleus and harbors transcription-activating potential. Knock-down of LBD13 expression by RNA interference resulted in reduced LR formation, whereas overexpression of LBD13 enhanced LR formation in transgenic Arabidopsis. Analysis of β-glucuronidase (GUS) expression under the control of the LBD13 promoter showed that GUS staining was detected in LRs emerged from the primary root, but not in LR primordia. Moreover, both the distribution of LR primordium number and developmental kinetics of LR primordia were not affected either by knock-down or by overexpression of LBD13. Taken together, these results suggest that LBD13 is a nuclear-localized transcriptional activator and controls LR formation during or after LR emergence.

Rice transcription factor OsMADS25 modulates root growth and confers salinity tolerance via the ABA-mediated regulatory pathway and ROS scavenging

Plant roots are constantly exposed to a variety of abiotic stresses, and high salinity is one of the major limiting conditions that impose constraints on plant growth. In this study, we describe that OsMADS25 is required for the root growth as well as salinity tolerance, via maintaining ROS homeostasis in rice (Oryza sativa). Overexpression of OsMADS25 remarkably enhanced the primary root (PR) length and lateral root (LR) density, whereas RNAi silence of this gene reduced PR elongation significantly, with altered ROS accumulation in the root tip. Transcriptional activation assays indicated that OsMADS25 activates OsGST4 (glutathione S–transferase) expression directly by binding to its promoter. Meanwhile, osgst4 mutant exhibited repressed growth and high sensitivity to salinity and oxidative stress, and recombinant OsGST4 protein was found to have ROS–scavenging activity in vitro. Expectedly, overexpression of OsMADS25 significantly enhanced the tolerance to salinity and oxidative stress in rice plants, with the elevated activity of antioxidant enzymes, increased accumulation of osmoprotective solute proline and reduced frequency of open stoma. Furthermore, OsMADS25 specifically activated the transcription of OsP5CR, a key component of proline biosynthesis, by binding to its promoter. Interestingly, overexpression of OsMADS25 raised the root sensitivity to exogenous ABA, and the expression of ABA–dependent stress–responsive genes was elevated greatly in overexpression plants under salinity stress. In addition, OsMADS25 seemed to promote auxin signaling by activating OsYUC4 transcription. Taken together, our findings reveal that OsMADS25 might be an important transcriptional regulator that regulates the root growth and confers salinity tolerance in rice via the ABA–mediated regulatory pathway and ROS scavenging.

Plant roots are constantly exposed to a variety of abiotic stresses, and high salinity is one of major limiting conditions that impose constraints on plant growth. Here, we show that transcription factor OsMADS25 positively regulates the root system development and tolerance to salinity and oxidative stress in rice plants. We also provide strong evidence that OsMADS25 increases the ROS-scavenging capacity and proline accumulation by activating the expression of OsGST4 and OsP5CR directly. Moreover, OsMADS25 promotes ABA–dependent abiotic stress–responsive regulatory pathway. In addition, OsMADS25 seems to promote auxin signaling by activating OsYUC4 transcription. Overall, enhanced antioxidant responses and proline accumulation via the ABA–mediated regulatory pathway, have been proposed to be crucial for OsMADS25 to regulate the salinity tolerance in rice plants.