Cloning and Functional Analysis of Dwarf Gene Mini Plant 1 (MNP1) in Medicago truncatula

Mechanism of the Pulvinus-Driven Leaf Movement: An Overview

Leaf movement is a manifestation of plant response to the changing internal and external environment, aiming to optimize plant growth and development. Leaf movement is usually driven by a specialized motor organ, the pulvinus, and this movement is associated with different changes in volume and expansion on the two sides of the pulvinus. Blue light, auxin, GA, H+-ATPase, K+, Cl-, Ca2+, actin, and aquaporin collectively influence the changes in water flux in the tissue of the extensor and flexor of the pulvinus to establish a turgor pressure difference, thereby controlling leaf movement. However, how these factors regulate the multicellular motility of the pulvinus tissues in a species remains obscure. In addition, model plants such as Medicago truncatula, Mimosa pudica, and Samanea saman have been used to study pulvinus-driven leaf movement, showing a similarity in their pulvinus movement mechanisms. In this review, we summarize past research findings from the three model plants, and using Medicago truncatula as an example, suggest that genes regulating pulvinus movement are also involved in regulating plant growth and development. We also propose a model in which the variation of ion flux and water flux are critical steps to pulvinus movement and highlight questions for future research.

Important Factors Controlling Gibberellin Homeostasis in Plant Height Regulation

Plant height is an important agronomic trait that is closely associated with crop yield and quality. Gibberellins (GAs), a class of highly efficient plant growth regulators, play key roles in regulating plant height. Increasing reports indicate that transcriptional regulation is a major point of regulation of the GA pathways. Although substantial knowledge has been gained regarding GA biosynthetic and signaling pathways, important factors contributing to the regulatory mechanisms homeostatically controlling GA levels remain to be elucidated. Here, we provide an overview of current knowledge regarding the regulatory network involving transcription factors, noncoding RNAs, and histone modifications involved in GA pathways. We also discuss the mechanisms of interaction between GAs and other hormones in plant height development. Finally, future directions for applying knowledge of the GA hormone in crop breeding are described.

SlZF3 regulates tomato plant height by directly repressing SlGA20ox4 in the gibberellic acid biosynthesis pathway

Plant height is an important target trait for crop genetic improvement. Our previous work has identified a salt-tolerant C2H2 zinc finger, SlZF3, and its overexpression lines also showed a semi-dwarf phenotype, but the molecular mechanism remains to be elucidated. Here, we characterized the dwarf phenotype in detail. The dwarfism is caused by a decrease in stem internode cell elongation and deficiency of bioactive gibberellic acids (GAs), and can be rescued by exogenous GA3 treatment. Gene expression assays detected reduced expression of genes in the GA biosynthesis pathway of the overexpression lines, including SlGA20ox4. Several protein-DNA interaction methods confirmed that SlZF3 can directly bind to the SlGA20ox4 promoter and inhibit its expression, and the interaction can also occur for SlKS and SlKO. Overexpression of SlGA20ox4 in the SlZF3-overexpressing line can recover the dwarf phenotype. Therefore, SlZF3 regulates plant height by directly repressing genes in the tomato GA biosynthesis pathway.

Effects of gibberellins on important agronomic traits of horticultural plants

Horticultural plants such as vegetables, fruits, and ornamental plants are crucial to human life and socioeconomic development. Gibberellins (GAs), a class of diterpenoid compounds, control numerous developmental processes of plants. The roles of GAs in regulating growth and development of horticultural plants, and in regulating significant progress have been clarified. These findings have significant implications for promoting the quality and quantity of the products of horticultural plants. Here we review recent progress in determining the roles of GAs (including biosynthesis and signaling) in regulating plant stature, axillary meristem outgrowth, compound leaf development, flowering time, and parthenocarpy. These findings will provide a solid foundation for further improving the quality and quantity of horticultural plants products.

Enabling Medicago truncatula forward genetics: identification of genetic crossing partner for R108 and development of mapping resources for Tnt1 mutants

Though Medicago truncatula Tnt1 mutants are widely used by researchers in the legume community, they are mainly used for reverse genetics because of the availability of the BLAST-searchable large-scale flanking sequence tags database. However, these mutants should have also been used extensively for forward genetic screens, an effort that has been hindered due to the lack of a compatible genetic crossing partner for the M. truncatula genotype R108, from which Tnt1 mutants were generated. In this study, we selected three Medicago HapMap lines (HM017, HM018 and HM022) and performed reciprocal genetic crosses with R108. After phenotypic analyses in F1 and F2 progenies, HM017 was identified as a compatible crossing partner with R108. By comparing the assembled genomic sequences of HM017 and R108, we developed and confirmed 318 Indel markers evenly distributed across the eight chromosomes of the M. truncatula genome. To validate the effectiveness of these markers, by employing the map-based cloning approach, we cloned the causative gene in the dwarf mutant crs isolated from the Tnt1 mutant population, identifying it as gibberellin 3-β-dioxygenase 1, using some of the confirmed Indel markers. The primer sequences and the size difference of each marker were made available for users in the web-based database. The identification of the crossing partner for R108 and the generation of Indel markers will enhance the forward genetics and the overall usage of the Tnt1 mutants.

Comparative Analysis of Codon Bias in the Chloroplast Genomes of Theaceae Species

Theaceae species are dicotyledonous angiosperms with extremely high ornamental and economic value. The chloroplast genome is traditionally used to study species evolution, expression of chloroplast genes and chloroplast transformation. Codon usage bias (CUB) analysis is beneficial for investigations of evolutionary relationships and can be used to improve gene expression efficiency in genetic transformation research. However, there are relatively few systematic studies of the CUB in the chloroplast genomes of Theaceae species. In this study, CUB and nucleotide compositions parameters were determined by the scripts written in the Perl language, CodonW 1.4.2, CU.Win2000, RStudio and SPSS 23.0. The chloroplast genome data of 40 Theaceae species were obtained to analyse the codon usage (CU) characteristics of the coding regions and the influence of the source of variation on CUB. To explore the relationship between the CUB and gene expression levels in these 40 Theaceae plastomes, the synonymous codon usage order (SCUO) and measure independent of length and composition (MILC) values were determined. Finally, phylogenetic analysis revealed the genetic evolutionary relationships among these Theaceae species. Our results showed that based on the chloroplast genomes of these 40 Theaceae species, the CUB was for codons containing A/T bases and those that ended with A/T bases. Moreover, there was great commonality in the CUB of the Theaceae species according to comparative analysis of relative synonymous codon usage (RSCU) and relative frequency of synonymous codon (RFSC): these species had 29 identical codons with bias (RSCU > 1), and there were 19 identical high-frequency codons. The CUB of Theaceae species is mainly affected by natural selection. The SCUO value of the 40 Theaceae species was 0.23 or 0.24, and the chloroplast gene expression level was moderate, according to MILC values. Additionally, we observed a positive correlation between the SCUO and MILC values, which indicated that CUB might affect gene expression. Furthermore, the phylogenetic analysis showed that the evolutionary relationships in these 40 Theaceae species were relatively conserved. A systematic study on the CUB and expression of Theaceae species provides further evidence for their evolution and phylogeny.

The Genetic Control of the Compound Leaf Patterning in Medicago truncatula

Simple and compound which are the two basic types of leaves are distinguished by the pattern of the distribution of blades on the petiole. Compared to simple leaves comprising a single blade, compound leaves have multiple blade units and exhibit more complex and diverse patterns of organ organization, and the molecular mechanisms underlying their pattern formation are receiving more and more attention in recent years. Studies in model legume Medicago truncatula have led to an improved understanding of the genetic control of the compound leaf patterning. This review is an attempt to summarize the current knowledge about the compound leaf morphogenesis of M. truncatula, with a focus on the molecular mechanisms involved in pattern formation. It also includes some comparisons of the molecular mechanisms between leaf morphogenesis of different model species and offers useful information for the molecular design of legume crops.

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

Plant height is an important agronomic trait that is closely related to biomass yield and crop production. Despite legumes comprise one of the largest monophyletic families that are second only to grasses in terms of economic and nutritional values, due to an ancient genome duplication event, most legume plants have complex genomes, thus the molecular mechanisms that determine plant height are less known in legumes. Here, we report the identification and characterization of MAIN STEM DWARF1 (MSD1), which is required for the plant height in the model legume Medicago truncatula. Loss of function of MSD1 leads to severely reduced main stem height but normal lateral branch elongation in M. truncatula. Histological analysis revealed that the msd1-1 main stem has shorter internodes with reduced cell size and number compared with the wild type, indicating that MSD1 affects cell elongation and cell proliferation. MSD1 encodes a putative GA 20-oxidase that is expressed at significantly higher levels in the main shoot apex than in the lateral shoot apices, suggesting that MSD1 expression is associated with its effect on the main stem elongation. UPLC-MS/MS analysis showed that GA₉ and GA₄, two identified products of the GA 20-oxidase, were severely reduced in msd1-1, and the dwarf phenotype of msd1-1 could be rescued by supplementation with gibberellic acid GA₃, confirming that MSD1 functions as a biologically active GA 20-oxidase. Moreover, we found that disruption of either MtGA20ox7 or MtGA20ox8, homologs of MSD1, has little effects on the elongation of the main stem, while the msd1-1 mtga20ox7-1 mtga20ox8 triple mutants exhibits a severe short main shoot and lateral branches, as well as reduced leaf size, suggesting that MSD1 and its homologs MtGA20ox7 and MtGA20ox8, redundantly regulate M. truncatula shoot elongation and leaf development. Taken together, our findings demonstrate the molecular mechanism of MSD1-mediated regulation of main stem elongation in M. truncatula and provide insights into understanding the functional diversity of GA 20-oxidases in optimizing plant architecture in legumes.