Harmony but Not Uniformity: Role of Strigolactone in Plants

Strigolactones and Shoot Branching: What Is the Real Hormone and How Does It Work?

There have been substantial advances in our understanding of many aspects of strigolactone regulation of branching since the discovery of strigolactones as phytohormones. These include further insights into the network of phytohormones and other signals that regulate branching, as well as deep insights into strigolactone biosynthesis, metabolism, transport, perception and downstream signaling. In this review, we provide an update on recent advances in our understanding of how the strigolactone pathway co-ordinately and dynamically regulates bud outgrowth and pose some important outstanding questions that are yet to be resolved.

New Series of Zaxinone Mimics (MiZax) for Fundamental and Applied Research

The apocarotenoid zaxinone is a recently discovered regulatory metabolite required for proper rice growth and development. In addition, zaxinone and its two mimics (MiZax3 and MiZax5) were shown to have a remarkable growth-promoting activity on crops and a capability to reduce infestation by the root parasitic plant Striga through decreasing strigolactone (SL) production, suggesting their potential for application in agriculture and horticulture. In the present study, we developed a new series of MiZax via structural modification of the two potent zaxinone mimics (MiZax3 and MiZax5) and evaluated their effect on plant growth and Striga infestation. In general, the structural modifications to MiZax3 and MiZax5 did not additionally improve their overall performance but caused an increase in certain activities. In conclusion, MiZax5 and especially MiZax3 remain the likely most efficient zaxinone mimics for controlling Striga infestation.

How do arbuscular mycorrhizas affect reproductive functional fitness of host plants?

Arbuscular mycorrhizal (AM) symbiosis in soil may be directly or indirectly involved in the reproductive process of sexually reproducing plants (seed plants), and affect their reproductive fitness. However, it is not clear how underground AM symbiosis affects plant reproductive function. Here, we reviewed the studies on the effects of AM symbiosis on plant reproductive fitness including both male function (pollen) and female function (seed). AM symbiosis regulates the development and function of plant sexual organs by affecting the nutrient using strategy and participating in the formation of hormone networks and secondary compounds in host plants. The nutrient supply (especially phosphorus supply) of AM symbiosis may be the main factor affecting plant's reproductive function. Moreover, the changes in hormone levels and secondary metabolite content induced by AM symbiosis can also affect host plants reproductive fitness. These effects can occur in pollen formation and transport, pollen tube growth and seed production, and seedling performance. Finally, we discuss other possible effects of AM symbiosis on the male and female functional fitness, and suggest several additional factors that may be involved in the influence of AM symbiosis on the reproductive fitness of host plants. We believe that it is necessary to accurately identify and verify the mechanisms driving the changes of reproductive fitness of host plant in symbiotic networks in the future. A more thorough understanding of the mechanism of AM symbiosis on reproductive function will help to improve our understanding of AM fungus ecological roles and may provide references for improving the productivity of natural and agricultural ecosystems.

Genome wide analysis of DWARF27 genes in soybean and functional characterization of GmD27c reveals eminent role of strigolactones in rhizobia interaction and nodulation in Glycine max

BACKGROUND

Strigolactones (SLs) are newly identified hormones and their biosynthesis is stimulated under phosphate deprivation and accomplished by the action of several enzymes, including the beta-carotene isomerase DWARF27 (D27). Expression of D27 is well renowned to respond to phosphate insufficiency. However, the identification and functional analysis of the carotenoid isomerase D27 genes are not elucidated in soybean.

METHODS AND RESULTS

A total of six D27 genes were identified in the soybean genome and designated on the basis of chromosomal localization. According to the findings, these genes were irregularly distributed on chromosomes, and segmental repetition led to the expansion of the soybean GmD27 gene family. Based on a neighbor-joining phylogenetic tree, the predicted D27 proteins of soybean were divided into three clades. Based on RNA seq data analysis, GmD27 genes were differently expressed in various tissues but GmD27c was the highest. Therefore, GmD27c was chosen for the additional functional study due to its rather obvious transcription in nodulation and roots. RT-qPCR results showed that GmD27c was highly expressed in different nodule stages and in response to rhizobia infection. Functional characterization of GmD27c revealed that overexpression of GmD27c led to higher nodule number, while GmD27c knockdown caused fewer nodules compared to GUS control. Furthermore, GmD27c overexpressed and knockdown lines oppositely regulated the expression of numerous nodulation genes, which are vital for the development of nodules.

CONCLUSION

This study not only discovered that SL biosynthesis and signaling pathway genes are conserved, but it also revealed that SL biosynthesis gene GmD27c and legume rhizobia have close interactions in controlling plant nodule number.

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives

Plants often face incompatible growing environments like drought, salinity, cold, frost, and elevated temperatures that affect plant growth and development leading to low yield and, in worse circumstances, plant death. The arsenal of versatile compounds for plant consumption and structure is called metabolites, which allows them to develop strategies to stop enemies, fight pathogens, replace their competitors and go beyond environmental restraints. These elements are formed under particular abiotic stresses like flooding, heat, drought, cold, etc., and biotic stress such as a pathogenic attack, thus associated with survival strategy of plants. Stress responses of plants are vigorous and include multifaceted crosstalk between different levels of regulation, including regulation of metabolism and expression of genes for morphological and physiological adaptation. To date, many of these compounds and their biosynthetic pathways have been found in the plant kingdom. Metabolites like amino acids, phenolics, hormones, polyamines, compatible solutes, antioxidants, pathogen related proteins (PR proteins), etc. are crucial for growth, stress tolerance, and plant defense. This review focuses on promising metabolites involved in stress tolerance under severe conditions and events signaling the mediation of stress-induced metabolic changes are presented.