Roles of Abscisic Acid and Gibberellins in Stem/Root Tuber Development

Tuber, or not tuber: Molecular and morphological basis of underground storage organ development

Underground storage organs occur in phylogenetically diverse plant taxa and arise from multiple tissue types including roots and stems. Thickening growth allows underground storage organs to accommodate carbohydrates and other nutrients and requires proliferation at various lateral meristems followed by cell expansion. The WOX-CLE module regulates thickening growth via the vascular cambium in several eudicot systems, but the molecular mechanisms of proliferation at other lateral meristems are not well understood. In potato, onion, and other systems, members of the phosphatidylethanolamine-binding protein (PEBP) gene family induce underground storage organ development in response to photoperiod cues. While molecular mechanisms of tuber development in potato are well understood, we lack detailed mechanistic knowledge for the extensive morphological and taxonomic diversity of underground storage organs in plants.

Transcriptomic profiling and discovery of key transcription factors involved in adventitious roots formation from root cuttings of mulberry

ARs plays a crucial role in plant morphogenesis and development. The limited and inefficient rooting of scions poses a significant challenge to the efficiency and quality of clonal propagation of forest trees in silvicultural practices. Building on previous research conducted by our team, we found that applying IBA at a concentration of 1000 mg/L significantly enhanced mulberry rooting. This study aims to uncover the molecular mechanisms underlying this effect by analyzing RNA sequencing data from mulberry phloem before and after treatment with IBA over time intervals of 10, 20, 30, and 40 days. We identified 5226 DEGs, which were then classified into GO terms and KEGG pathways, showing significant enrichment in hormone signaling processes. Using WGCNA, we identified eight co-expression modules, two of which were significantly correlated with the IBA treatment. Additionally, 18 transcription factors that potentially facilitate ARs formation in mulberry were identified, and an exploratory analysis on the cis-regulatory elements associated with these transcription factors was conducted. The findings of this study provide a comprehensive understanding of the mechanisms of ARs in mulberry and offer theoretical support for the discovery and utilization of exceptional genetic resources within the species.

Integrated transcriptomic and proteomic analysis of exogenous abscisic acid regulation on tuberous root development in Pseudostellaria heterophylla

Abscisic acid (ABA) significantly regulates plant growth and development, promoting tuberous root formation in various plants. However, the molecular mechanisms of ABA in the tuberous root development of Pseudostellaria heterophylla are not yet fully understood. This study utilized Illumina sequencing and de novo assembly strategies to obtain a reference transcriptome associated with ABA treatment. Subsequently, integrated transcriptomic and proteomic analyses were used to determine gene expression profiles in P. heterophylla tuberous roots. ABA treatment significantly increases the diameter and shortens the length of tuberous roots. Clustering analysis identified 2,256 differentially expressed genes and 679 differentially abundant proteins regulated by ABA. Gene co-expression and protein interaction networks revealed ABA positively induced 30 vital regulators. Furthermore, we identified and assigned putative functions to transcription factors (PhMYB10, PhbZIP2, PhbZIP, PhSBP) that mediate ABA signaling involved in the regulation of tuberous root development, including those related to cell wall metabolism, cell division, starch synthesis, hormone metabolism. Our findings provide valuable insights into the complex signaling networks of tuberous root development modulated by ABA. It provided potential targets for genetic manipulation to improve the yield and quality of P. heterophylla, which could significantly impact its cultivation and medicinal value.

The tomato EAR-motif repressor, SlERF36, accelerates growth transitions and reduces plant life cycle by regulating GA levels and responses

Faster vegetative growth and early maturity/harvest reduce plant life cycle time and are important agricultural traits facilitating early crop rotation. GA is a key hormone governing developmental transitions that determine growth speed in plants. An EAR-motif repressor, SlERF36 that regulates various growth transitions, partly through regulation of the GA pathway and GA levels, was identified in tomato. Suppression of SlERF36 delayed germination, slowed down organ growth and delayed the onset of flowering time, fruit harvest and whole-plant senescence by 10-15 days. Its over-expression promoted faster growth by accelerating all these transitions besides increasing organ expansion and plant height substantially. The plant life cycle and fruit harvest were completed 20-30 days earlier than control without affecting yield, in glasshouse as well as net-house conditions, across seasons and generations. These changes in life cycle were associated with reciprocal changes in expression of GA pathway genes and basal GA levels between suppression and over-expression lines. SlERF36 interacted with the promoters of two GA2 oxidase genes, SlGA2ox3 and SlGA2ox4, and the DELLA gene, SlDELLA, reducing their transcription and causing a 3-5-fold increase in basal GA3/GA4 levels. Its suppression increased SlGA2ox3/4 transcript levels and reduced GA3/GA4 levels by 30%-50%. SlERF36 is conserved across families making it an important candidate in agricultural and horticultural crops for manipulation of plant growth and developmental transitions to reduce life cycles for faster harvest.

Mitigating chromium toxicity in rice (Oryza sativa L.) via ABA and 6-BAP: Unveiling synergistic benefits on morphophysiological traits and ASA-GSH cycle

In recent years, the use of plant hormones, such as abscisic acid (ABA) and 6-benzylaminopurine (6-BAP), has gained significant attention for their role in mitigating abiotic stresses across various plant species. These hormones have been shown to play a vital role in enhancing the ascorbate-glutathione cycle and eliciting a wide range of plant growth and biomass, photosynthetic efficiency, oxidative stress and response of antioxidants and other physiological responses. While previous research has been conducted on the individual impact of ABA and 6-BAP in metal stress resistance among various crop species, their combined effects in the context of heavy metal-stressed conditions remain underexplored. The current investigation is to assess the beneficial effects of single and combined ABA (5 and 10 μM L-1) and 6-BAP (5 and 10 μM L-1) applications in rice (Oryza sativa L.) cultivated in chromium (Cr)-contaminated soil (100 μM). Our results showed that the Cr toxicity in the soil showed a significant declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in O. sativa. However, Cr toxicity significantly increased oxidative stress biomarkers, organic acids, enzymatic and non-enzymatic antioxidants including their gene expression in O. sativa seedlings. Although, the application of ABA and 6-BAP showed a significant increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, And Cr uptake. In addition, individual or combined application of ABA and 6-BAP enhanced the cellular fractionation and decreases the proline metabolism and AsA-GSH cycle in rice plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Characterization and expression analysis of SnRK2, PYL, and ABF/ AREB/ ABI5 gene families in sweet potato

Abscisic acid (ABA) signaling in plants is essential to several aspects of plant development, such as tolerance to environmental stresses and growth. ABA signaling is also important for storage organ formation in crops, such as sweet potato. However, the repertoire of I. batatas ABA signaling gene families has not yet been fully characterized, so that it is unclear which members of these families are necessary for tuberization. Therefore, genome-wide identification of the sweet potato ABF/ AREB/ ABI5, SnRK2, and PYL gene families was performed, along with phylogenetic, motif, cis-regulatory element (CRE), and expression analyses. Nine ABF, eight SnRK2, and eleven PYL gene family members were identified, and there was high sequence conservation among these proteins that were revealed by phylogenetic and motif analyses. The promoter sequences of these genes had multiple CREs that were involved in hormone responses and stress responses. In silico and qRT-PCR expression analyses revealed that these genes were expressed in various tissues and that IbABF3, IbABF4, IbDPBF3, IbDPBF4, IbPYL4, IbSnRK2.1, and IbSnRK2.2 were significantly expressed during storage root development. These results are an important reference that can be used for functional validation studies to better understand how ABA signaling elicits storage root formation at the molecular level.

Physiological, anatomical and quality indexes of root tuber formation and development in chayote (Sechium edule)

BACKGROUND

Chayote is an underutilized species of Cucurbitaceae. It is rich in nutrients such as protein, minerals, phenols and its extracts have anti-cardiovascular and anti-cancer effects, making it a versatile plant for both medicinal and culinary purposes. Although research on its root tuber is limited, they are rich in starch and have a structure similar to that of potatoes, cassava, and sweet potatoes. Therefore, they can serve as potential substitutes for potatoes and offer promising prospects as agricultural and industrial resources. However, the physiological and cellular mechanisms of chayote root tuber formation and development are still unclear.

RESULTS

In this study, we observed the growth habit of 'Tuershao' (high yield of root tuber). The results revealed that the tuber enlargement period of 'Tuershao' lasts approximately 120 days, with the early enlargement phase occurring during 0-30 days, rapid enlargement phase during 30-90 days, and maturation phase during 90-120 days. Physiological indicators demonstrated a gradual increase in starch content as the tuber developed. The activities of sucrose synthase (SUS) and invertase (VIN) showed a consistent trend, reaching the highest level in the rapid expansion period, which was the key enzyme affecting tuber expansion. Moreover, the special petal like structure formed by the secondary phloem and secondary xylem of the tuber resulted in its enlargement, facilitating the accumulation of abundant starch within the thin-walled cells of this structure. Principal component analysis further confirmed that starch content, SUS and VIN activities, as well as the concentrations of calcium (Ca), iron (Fe), and selenium (Se), were the major factors influencing tuber development. Moreover, the low temperature environment not only promoted the growth of 'Tuershao' tubers but also enhanced the accumulation of nutritional substances.

CONCLUSIONS

These findings contribute to a deeper understanding of the formation and developmental mechanisms of 'Tuershao' tubers, providing valuable guidance for cultivation practices aimed at improving crop yield.

Deciphering the hormone regulatory mechanisms of storage root initiation in sweet potato: challenges and future prospects

Sweet potato (Ipomoea batatas) is an economically important food crop that is grown primarily for its edible storage roots. Several researchers have consequently been conducting studies to increase sweet potato yield, and an important aspect of this research involves understanding how storage root initiation occurs. Although significant progress has been made, several challenges associated with studying this crop have resulted in lagging progress compared to other crops and thus sweet potato storage root initiation is not clearly understood. This article highlights the most important aspects of the hormone signalling processes during storage root initiation that needs to be investigated further and suggests candidate genes that should be prioritized for further study, based on their importance in storage organ formation in other crops. Lastly, ways of overcoming the challenges associated with studying this crop are suggested.

Combining Metabolomics and Transcriptomics to Reveal the Regulatory Mechanism of Taproot Enlargement in Panax ginseng

Ginseng is regarded as the “king of herbs” in China, with its roots and rhizomes used as medicine, and it has a high medicinal value. In order to meet the market demand, the artificial cultivation of ginseng emerged, but different growth environments significantly affect the root morphology of garden ginseng. In this study, we used ginseng cultivated in deforested land (CF-CG) and ginseng cultivated in farmland (F-CG) as experimental materials. These two phenotypes were explored at the transcriptomic and metabolomic levels so as to understand the regulatory mechanism of taproot enlargement in garden ginseng. The results show that, compared with those of F-CG, the thickness of the main roots in CF-CG was increased by 70.5%, and the fresh weight of the taproots was increased by 305.4%. Sucrose, fructose and ginsenoside were significantly accumulated in CF-CG. During the enlargement of the taproots of CF-CG, genes related to starch and sucrose metabolism were significantly up-regulated, while genes related to lignin biosynthesis were significantly down-regulated. Auxin, gibberellin and abscisic acid synergistically regulated the enlargement of the taproots of the garden ginseng. In addition, as a sugar signaling molecule, T6P might act on the auxin synthesis gene ALDH2 to promote the synthesis of auxin and, thus, participate in the growth and development of garden ginseng roots. In summary, our study is conducive to clarifying the molecular regulation mechanism of taproot enlargement in garden ginseng, and it provides new insights for the further exploration of the morphogenesis of ginseng roots.

Combined analysis of the transcriptome and metabolome provides insights into the fleshy stem expansion mechanism in stem lettuce

As a stem variety of lettuce, the fleshy stem is the main product organ of stem lettuce. The molecular mechanism of fleshy stem expansion in stem lettuce is a complex biological process. In the study, the material accumulation, gene expression, and morphogenesis during fleshy stem expansion process were analyzed by the comparative analysis of metabolome, transcriptome and the anatomical studies. The anatomical studies showed that the occurrence and activity of vascular cambium mainly led to the development of fleshy stems; and the volume of pith cells gradually increased and arranged tightly during the expansion process. A total of 822 differential metabolites and 9,383 differentially expressed genes (DEGs) were identified by the metabolomics and transcriptomics analyses, respectively. These changes significantly enriched in sugar synthesis, glycolysis, and plant hormone anabolism. The expression profiles of genes in the sugar metabolic pathway gradually increased in fleshy stem expansion process. But the sucrose content was the highest in the early stage of fleshy stem expansion, other sugars such as fructose and glucose content increased during fleshy stem expansion process. Plant hormones, including IAA, GA, CTK, and JA, depicted important roles at different stem expansion stages. A total of 1,805 DEGs were identified as transcription factors, such as MYB, bHLH, and bZIP, indicating that these transcription factor families might regulate the fleshy stems expansion in lettuce. In addition, the expression patterns identified by qRT-PCR were consistent with the expression abundance identified by the transcriptome data. The important genes and metabolites identified in the lettuce fleshy stem expansion process will provide important information for the further molecular mechanism study of lettuce fleshy stem growth and development.

Plant Development and Crop Yield: The Role of Gibberellins

Gibberellins have been classically related to a few key developmental processes, thus being essential for the accurate unfolding of plant genetic programs. After more than a century of research, over one hundred different gibberellins have been described. There is a continuously increasing interest in gibberellins research because of their relevant role in the so-called "Green Revolution", as well as their current and possible applications in crop improvement. The functions attributed to gibberellins have been traditionally restricted to the regulation of plant stature, seed germination, and flowering. Nonetheless, research in the last years has shown that these functions extend to many other relevant processes. In this review, the current knowledge on gibberellins homeostasis and mode of action is briefly outlined, while specific attention is focused on the many different responses in which gibberellins take part. Thus, those genes and proteins identified as being involved in the regulation of gibberellin responses in model and non-model species are highlighted. The present review aims to provide a comprehensive picture of the state-of-the-art perception of gibberellins molecular biology and its effects on plant development. This picture might be helpful to enhance our current understanding of gibberellins biology and provide the know-how for the development of more accurate research and breeding programs.