Advances in micropropagation, somatic embryogenesis, somatic hybridizations, genetic transformation and cryopreservation for Passiflora improvement.

Passion fruit is an essential commercial plant in the tropics and subtropics, which has lately seen a rise in demand for high-quality fruits and large-scale production. Generally, different species of passion fruit (Passiflora sp.) are propagated by sexual reproduction. However, asexual reproduction, such as stem cuttings, grafting, or tissue culture, is also available and advantageous in many instances. Recent research on passion fruit has concentrated on improving and establishing methodologies for embryogenesis, clonal proliferation via (somatic embryos), homozygote regeneration (by anther culture), germplasm preservation (via cryopreservation), and genetic transformation. These developments have resulted in potentially new directions for asexual propagation. Even though effective embryo culture and cryogenics are now available, however the limited frequency of embryogenic callus transformation to ex-vitro seedlings still restricts the substantial clonal replication of passion fruit. Here, in this review the advancement related to biotechnological approaches and the current understanding of Passiflora tissue culture. In vitro culture, organogenesis, cryopreservation, breeding, and productivity of Passiflora will significantly improve with novel propagation approaches, which could be applied to a wider range of germplasm.

Genome-wide identification of miRNAs and targets associated with cell wall biosynthesis: Differential roles of dlo-miR397a and dlo-miR408-3p during early somatic embryogenesis in longan.

The dynamic alterations in cell wall (CW) biosynthesis play an essential role in physiological isolation during the plant somatic embryogenesis (SE). However, the mechanisms underlying the functions of cell wall-associated miRNAs (CW-miRNA) remain poorly understood in plant SE. Here, we have identified 36 distinct candidate miRNAs associated with CW biosynthesis from longan third-generation genome as well as miRNA transcriptome, and modified RLM-RACE validated four distinct miRNA, which specifically targeted four CW-related genes. More importantly, we found that the dlo-miR397a-antagomir significantly enhanced DlLAC7 expression and improved laccase activity. Interestingly, inhibition of dlo-miR397a increased CW lignin deposition and promoted the tightening of protodermal cell by miRNA-mimic technology during early SE. Moreover, overexpression of dlo-miR408-3p (dlo-miR408-3p-agomir) markedly decreased DlLAC12 expression. dlo-miR408-3p-agomir activated rapid cell division, thus promoting the globular embryo (GE) development, which might be due to high DNA synthesis activity in protoepidermal cells, rather than affecting lignin synthesis. The subcellular location also indicated that both DlLAC7 and DlLAC12 proteins were primarily localized in CW and regulated CW biosynthesis. Overall, our findings provided new insight on the molecular regulatory networks comprising various miRNAs associated with cell wall, and established that dlo-miR397a and dlo-miR408-3p played differential roles during early SE in longan. The findings also shed some light on the potential role of miRNA target DlLAC regulating in vivo embryonic development of plant.

Comparative Expression Profiling of Snf2 Family Genes During Reproductive Development and Stress Responses in Rice.

Sucrose non-fermenting 2 (Snf2) protein family, as chromatin remodeling factors, is an enormous and the most diverse protein family, which contributes to biological processes of replication, transcription, and DNA repair using the energy of adenosine triphosphate (ATP) hydrolysis. The members of Snf2 family proteins have been well characterized in Arabidopsis, rice, and tomato. Although this family received significant attention, few genes were identified uniquely for their roles in mediating reproductive development and stress tolerance in rice. In the present study, we comprehensively analyzed the expression profiling of Snf2 genes during reproductive development and biotic/abiotic stresses. Our results showed that five proteins (OsCHR712/715/720/726/739) were mainly localized in the nucleus, while OsCHR715/739 were also slightly expressed in the cell membrane. There were abundant cis-acting elements in the putative promoter of Snf2 genes, including dehydration, MeJA, MYB binding site for drought, ABA-responsive, and stress-responsive element. Most of the genes were induced immediately after Magnaporthe oryzae infection at 12 h post-infection (hpi). About 55% of the total genes were upregulated under salt and drought stresses during the entire time, and 22-35% of the total genes were upregulated at 3 h. It was noteworthy that the seven genes (OsCHR705, OsCHR706, OsCHR710, OsCHR714, OsCHR721, OsCHR726, and OsCHR737) were upregulated, and one gene (OsCHR712) was downregulated under salt and drought stresses, respectively. The deficiency of OsCHR726 mutations displayed a hypersensitive phenotype under salt stress. These results will be significantly useful features for the validation of the rice Snf2 genes and facilitate understanding of the genetic engineering of crops with improved biotic and abiotic stresses.

OsDDM1b Controls Grain Size by Influencing Cell Cycling and Regulating Homeostasis and Signaling of Brassinosteroid in Rice.

Snf2 family proteins are the crucial subunits of chromatin-remodeling complexes (CRCs), which contributes to the biological processes of transcription, replication, and DNA repair using ATP as energy. Some CRC subunits have been confirmed to be the critical regulators in various aspects of plant growth and development and in epigenetic mechanisms such as histone modification, DNA methylation, and histone variants. However, the functions of Snf2 family genes in rice were poorly investigated. In this study, the relative expression profile of 40 members of Snf2 family in rice was studied at certain developmental stages of seed. Our results revealed that OsCHR741/OsDDM1b (Decrease in DNA methylation 1) was accumulated highly in the early developmental stage of seeds. We further analyzed the OsDDM1b T-DNA insertion loss-of-function of mutant, which exhibited dwarfism, smaller organ size, and shorter and wider grain size than the wild type (Hwayoung, HY), yet no difference in 1,000-grain weight. Consistent with the grain size, the outer parenchyma cell layers of lemma in osddm1b developed more cells with decreased size. OsDDM1b encoded a nucleus, membrane-localized protein and was distributed predominately in young spikelets and seeds, asserting its role in grain size. Meanwhile, the osddm1b was less sensitive to brassinosteroids (BRs) while the endogenous BR levels increased. We detected changes in the expression levels of the BR signaling pathway and feedback-inhibited genes with and without exogenous BR application, and the alterations of expression were also observed in grain size-related genes in the osddm1b. Altogether, our results suggest that OsDDM1b plays a crucial role in grain size via influencing cell proliferation and regulating BR signaling and homeostasis.

Towards Understanding the Involvement of H+-ATPase in Programmed Cell Death of Psammosilene tunicoides after Oxalic Acid Application.

Psammosilene tunicoides is a unique perennial medicinal plant species native to the Southwestern regions of China. Its wild population is rare and endangered due to over-excessive collection and extended growth (4-5 years). This research shows that H+-ATPase activity was a key factor for oxalate-inducing programmed cell death (PCD) of P. tunicoides suspension cells. Oxalic acid (OA) is an effective abiotic elicitor that enhances a plant cell's resistance to environmental stress. However, the role of OA in this process remains to be mechanistically unveiled. The present study evaluated the role of OA-induced cell death using an inverted fluorescence microscope after staining with Evans blue, FDA, PI, and Rd123. OA-stimulated changes in K+ and Ca2+ trans-membrane flows using a patch-clamp method, together with OA modulation of H+-ATPase activity, were further examined. OA treatment increased cell death rate in a dosage-and duration-dependent manner. OA significantly decreased the mitochondria activity and damaged its electron transport chain. The OA treatment also decreased intracellular pH, while the FC increased the pH value. Simultaneously, NH4Cl caused intracellular acidification. The OA treatment independently resulted in 90% and the FC led to 25% cell death rates. Consistently, the combined treatments caused a 31% cell death rate. Furthermore, treatment with EGTA caused a similar change in intracellular pH value to the La3+ and OA application. Combined results suggest that OA-caused cell death could be attributed to intracellular acidification and the involvement of OA in the influx of extracellular Ca2+, thereby leading to membrane depolarization. Here we explore the resistance mechanism of P. tunicoides cells against various stresses endowed by OA treatment.

ROS and Oxidative Response Systems in Plants Under Biotic and Abiotic Stresses: Revisiting the Crucial Role of Phosphite Triggered Plants Defense Response.

Phosphite (Phi) is a chemical analog of orthophosphate [HPO4 3-]. It is a systemic pesticide generally known to control the prevalence of oomycetes and soil-borne diseases such as Phytophthora, Pythium, and Plasmopora species. Phi can also control disease symptoms and the spread of pathogenic bacteria, fungi, and nematodes. Phi plays critical roles as a fungicide, pesticide, fertilizer, or biostimulator. Overall, Phi can alleviate the severity of the disease caused by oomycete, fungi, pathogenic bacteria, and nematodes (leave, stem, fruit, tuber, and root) in various plants (vegetables, fruits, crops, root/tuber crops, ornamental plants, and forests). Advance research in molecular, physiological, and biochemical approaches has approved the key role of Phi in enhancing crop growth, quantity, and quality of several plant species. Phi is chemically similar to orthophosphate, and inside the cells, it is likely to get involved in different features of phosphate metabolism in both plants and pathogens. In plants, a range of physiobiochemical alterations are induced by plant pathogen stress, which causes lowered photosynthesis activities, enzymatic activities, increased accumulation of reactive oxygen species (ROS), and modification in a large group of genes. To date, several attempts have been made to study plant-pathogen interactions with the intent to minimize the loss of crop productivity. Phi's emerging function as a biostimulant in plants has boost plant yield and tolerance against various stress factors. This review discusses Phi-mediated biostimulant effects against biotic and abiotic stresses.

Effects of phosphite as a plant biostimulant on metabolism and stress response for better plant performance in Solanum tuberosum.

Food availability represents a major worldwide concern due to population growth, increased demand, and climate change. Therefore, it is imperative to identify compounds that can improve crop performance. Plant biostimulants have gained prominence because of their potentials to increase germination, productivity and quality of a wide range of horticultural and agronomic crops. Phosphite (Phi), an analog of orthophosphate, is an emerging biostimulant used in horticulture and agronomy. The aim of this study was to uncover the molecular mechanisms through which Phi acts as a biostimulant with potential effects of overall plant growth. Field and greenhouse experiments, using 4 potato cultivars, showed that following Phi applications, plant performance, including several physio-biochemical traits, crop productivity, and quality traits, were significantly improved. RNA sequencing of control and Phi-treated plants of cultivar Xingjia No. 2, at 0 h, 6 h, 24 h, 48 h, 72 h and 96 h after the Phi application for 24 h revealed extensive changes in the gene expression profiles. A total of 2856 differentially expressed genes were identified, suggesting that multiple pathways of primary and secondary metabolism, such as flavonoids biosynthesis, starch and sucrose metabolism, and phenylpropanoid biosynthesis, were strongly influenced by foliar applications of Phi. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses associated with defense responses revealed significant effects of Phi on a plethora of defense mechanisms. These results suggest that Phi acted as a biostimulant by priming the plants, that was, by triggering dynamic changes in gene expression and modulating metabolic fluxes in a way that allowed plants to perform better. Therefore, Phi usage has the potential to improve crop yield and health, alleviating the challenges posed by the need of feeding a growing world population, while minimizing the agricultural impact on human health and environment.

Phosphite Application Alleviates Pythophthora infestans by Modulation of Photosynthetic and Physio-Biochemical Metabolites in Potato Leaves.

Potato late blight (Phytophtora infestans) is among the most severely damaging diseases of potato (Solanum tuberusom L.) worldwide, causing serious damages in potato leaves and tubers. In the present study, the effects of potassium phosphite (KPhi) applications on photosynthetic parameters, enzymatic and non-enzymatic antioxidant properties, hydrogen peroxide (H2O2) and malondialdehyde (MDA), total protein and total carbohydrate of potato leaves challenged with P. infestans pathogen were investigated. Potato leaves were sprayed five times with KPhi (0.5%) during the growing season prior to inoculation with P. infestans. The potato leaves were artificially infected by the LC06-44 pathogen isolate. The leaves were sampled at 0, 24, 48, 72 and 96 h after the infection for evaluations. P. infestans infection reduced chlorophyll (Chl) pigments contents, chlorophyll fluorescence, carotenoid (Car) and anthocyanin contents and increased the accumulation of H2O2 and MDA. Meanwhile, our result showed that KPhi treatment alleviated adverse effect of late blight in potato leaves. KPhi application also increased plant tolerance to the pathogen with improved photosynthetic parameters Chl a, b, total Chl, Car, and anthocyanin compare to controls. Moreover, the increased oxidative enzymes activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APx), and non-enzymatic substances such as phenolics, flavonoids and proline were found in KPhi treated plants, compared to untreated plants after inoculation. In addition, KPhi application followed by P. infestans infection also decreased the content of H2O2 and MDA, but increased the total protein and total carbohydrate contents in potato leaves. The consequence of current research indicated that KPhi played a vital role in pathogen tolerance, protecting the functions of photosynthetic apparatus by improved oxidative levels and physio-biochemical compounds in potato leaves.