Physiological and proteomic analysis reveals the impact of boron deficiency and surplus on alfalfa (Medicago sativa L.) reproductive organs

Tandem mass tag (TMT)-based quantitative proteomics analysis reveals the different responses of contrasting alfalfa varieties to drought stress

BACKGROUND

Drought stress restricts the growth, distribution and productivity of alfalfa (Medicago sativa L.). In order to study the response differences of alfalfa cultivars to drought stress, we previously carried out physiological and molecular comparative analysis on two alfalfa varieties with contrasting drought resistance (relatively drought-tolerant Longdong and drought-sensitive Algonquin). However, the differences in proteomic factors of the two varieties in response to drought stress still need to be further studied. Therefore, TMT-based quantitative proteomic analysis was performed using leaf tissues of the two alfalfa cultivars to identify and uncover differentially abundant proteins (DAPs).

RESULTS

In total, 677 DAPs were identified in Algonquin and 277 in Longdong under drought stress. Subsequently, we conducted various bioinformatics analysis on these DAPs, including subcellular location, functional classification and biological pathway enrichment. The first two main COG functional categories of DAPs in both alfalfa varieties after drought stress were 'Translation, ribosomal structure and biogenesis' and 'Posttranslational modification, protein turnover, chaperones'. According to KEGG database, the DAPs of the two alfalfa cultivars after drought treatment were differentially enriched in different biological pathways. The DAPs from Algonquin were enriched in 'photosynthesis' and 'ribosome'. The pathways of 'linoleic acid metabolism', 'protein processing in endoplasmic reticulum' and 'RNA transport' in Longdong were significantly enriched. Finally, we found significant differences in DAP enrichment and expression patterns between Longdong and Algonquin in glycolysis/glycogenesis, TCA cycle, photosynthesis, protein biosynthesis, flavonoid and isoflavonoid biosynthesis, and plant-pathogen interaction pathway after drought treatment.

CONCLUSIONS

The differences of DAPs involved in various metabolic pathways may explain the differences in the resistance of the two varieties to drought stress. These DAPs can be used as candidate proteins for molecular breeding of alfalfa to cultivate new germplasm with more drought tolerance to adapt to unfavorable environments.

Micronutrient deficiency-induced oxidative stress in plants

Micronutrients like iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), boron (B), nickel (Ni), and molybdenum (Mo) perform significant roles in the regulation of plant metabolism, growth, and development. Micronutrients, namely Fe, Zn, Cu, Mn, and Ni, are involved in oxidative stress and antioxidant defense as they are cofactors or activators of various antioxidant enzymes, viz., superoxide dismutase (Fe, Cu/Zn, Mn, and Ni), catalase (Fe), and ascorbate peroxidase (Fe). An effort has been made to incorporate recent advances along with classical work done on the micronutrient deficiency-induced oxidative stress and associated antioxidant responses of plants. Deficiency of a micronutrient produces ROS in the cellular compartments. Enzymatic and non-enzymatic antioxidant defense systems are often modulated by micronutrient deficiency to regulate redox balance and scavenge deleterious ROS for the safety of cellular constituents. ROS can strike cellular constituents such as lipids, proteins, and nucleic acids and can destruct cellular membranes and proteins. ROS might act as a signaling molecule and activate the antioxidant proteins by interacting with signaling partners such as respiratory burst oxidase homolog (RBOH), G-proteins, Ca2+, mitogen activated protein kinases (MAPKs), and various transcription factors (TFs). Opinions on probable ROS signaling under micronutrient deficiency have been described in this review. However, further research is required to decipher micronutrient deficiency-induced ROS generation, perception, and associated downstream signaling events, leading to the development of antioxidant responses in plants.

A critical review of plant adaptation to environmental boron stress: Uptake, utilization, and interplay with other abiotic and biotic factors

Boron (B) is an indispensable mineral nutrient for plants and is primarily taken up by roots mainly in the form of boric acid (H3BO3). Recently, research shows that B has a significant impact on plant growth and productivity due to its narrow range between deficiency and toxicity. Fertilization and other procedures to address B stress (deficiency and toxicity) in soils are generally expensive and time-consuming. Over the past 20 years, substantial studies have been conducted to investigate the mechanisms underlying B acquisition and the molecular regulation of B stress in plants. In this review, we discuss the effects of B stress on plant growth, physiology, and biochemistry, and finding on enhancing plant tolerance from the perspective of plant B uptake, transport, and utilization. We also refer to recent results demonstrating the interactions among B and other biological and abiotic factors, including nitrogen, phosphorus, aluminum, and microorganisms. Finally, emerging trends in this field are discussed.

Integrative analysis of transcriptome and metabolome revealed the mechanisms by which flavonoids and phytohormones regulated the adaptation of alfalfa roots to NaCl stress

INTRODUCTION

Salinity critically affects the growth and development of alfalfa (Medicago sativa), making it necessary to understand the molecular mechanism of alfalfa's adaptation to salt stress.

METHODS

In this study, alfalfa roots were subjected to salt stress and transcriptomics and metabolomics analyses were performed.

RESULTS

The results showed that flavonoid synthesis, hormone synthesis, and transduction pathways may be involved in the alfalfa salt stress adaptation reaction, and that they are related. Combined analysis of differential genes and differential metabolites found that dihydroquercetin and beta-ring hydroxylase (LUT5), ABA responsive element binding factor 2 (ABF2), protein phosphatase PP2C (PP2C) and abscisic acid (ABA) receptor PYL2 (PYL), luteolinidin was significantly correlated with PP2C and phytochrome-interacting factor 4 (PIF4) and (+)-7-isomethyl jasmonate were significantly correlated with flavonol synthase (FLS) gene. (+)-7-isomethyl jasmonate and homoeriodictyol chalcone were significantly correlated with peroxidase (POD). POD was significantly up-regulated under NaCl stress for 6 and 24 h. Moreover, flavonoids, gibberellin (GA), jasmonic acid (JA) and ABA were suggested to play an important role in alfalfa's response to salt stress. Further, GA,ABA, and JA may be involved in the regulation of flavonoids to improve alfalfa's salt tolerance, and JA may be a key signal to promote the synthesis of flavonoids.

DISCUSSION

This study revealed the possible molecular mechanism of alfalfa adaptation to salt stress, and identified a number of salt-tolerance candidate genes from the synthesis and signal transduction pathways of flavonoids and plant hormones, providing new insights into the regulatory network of alfalfa response to salt stress.

The regulation of plant lignin biosynthesis under boron deficiency conditions

Boron (B) is a required micronutrient that is crucial for the growth and development of vascular plants. A deficiency in B is generally regarded as a limiting factor affecting agricultural production in many parts of the world. Boron is involved in the metabolism of plant lignin and additionally, B deficiency can lead to the excessive accumulation of lignin in plant leaves/roots, resulting in corking symptoms and inhibited growth. However, the effect of B on lignin biosynthesis is not as well characterized as the specific function of B in the cell wall. In this article, recent studies on the regulation of lignin biosynthesis in plants under low-B stress conditions are reviewed. Moreover, the following possible mechanisms underlying the lignin synthesis promoted by B deficiency are discussed: (1) the accumulation of phenolic substances during B deficiency directly enhances lignin synthesis; (2) excess H₂ O₂ has a dual function to the enhancement of lignin under boron deficiency conditions, serving as a substrate and a signaling molecule; and (3) B deficiency regulates lignin synthesis through the expression of genes encoding transcription factors such as MYBs. Finally, future studies regarding physiology, molecules, and transcriptional regulation may reveal the mechanism(s) mediating the relationship between lignin synthesis and B deficiency. This review provides new insights and important references for future research and the enhancement of plant B nutrition.