Frontiers in Plant Science最新文献

Based on the totipotency and pluripotency of cells, plants are endowed with strong regenerative abilities. Light is a critical environmental factor influencing plant growth and development, playing an important role in plant regeneration. In this article, we provide a detailed summary of recent advances in understanding the effects of light on plant regeneration, with a focus on the fundamental processes and mechanisms involved in de novo shoot regeneration, somatic embryogenesis, and adventitious root formation. We focus on summarizing the effects of light intensity, light spectra, and photoperiod on these regeneration processes. Additionally, we propose the molecular mechanisms and regulatory networks underlying light-mediated plant regeneration. This article aims to deepen our understanding of the role of light in plant regeneration and to pave the way for future research on light-regulated regenerative processes in plants.

Huanglongbing (HLB) is a devastating citrus disease that threatens the citrus industry worldwide. HLB is associated with the bacteria Candidatus Liberibacter asiaticus (CLas) and as of today, there are no tools for economically viable disease management. Several wild Australian limes have been identified to be HLB resistant and their resistance is hypothesized to be conferred by resistance genes (R-genes), which mediate pathogen-specific defense responses. The aim of this study was to gain insight into the genomic features of R-genes in Australian limes, in comparison to susceptible citrus cultivars. In this study, we used five citrus genomes, including three Australian limes (Citrus australasica, C. glauca and C. inodora) and two cultivated citrus species (C. clementina and C. sinensis). Our results indicate up to 70% of the R-genes were identified in the unannotated regions in the original genome annotation of each species, owing to the use of a R-gene specific pipeline. Surprisingly, the two cultivated species harbored 15.8 to 104% more R-genes than the Australian limes. In all species, over 75% of the R-genes occurred in clusters and nearly 80% were concentrated in three chromosomes (Chr3, 5 and 7). The syntenic R-gene based phylogenic classification grouped the five species according to their HLB-resistance levels, reflecting the association between these R-genes and their distinct Australian origins. Domain structure analysis revealed substantial similarities in the R-genes between wild Australian limes and cultivated citrus. Investigation of chromosomal sites underlying Australian specific R genes revealed diversifying selection signatures on several chromosomal regions. The findings in this study will aid in the development of tools for genome-assisted breeding for HLB-resistant varieties.

Apomixis is a horticultural trait that enables clonal propagation of hybrids by producing asexual embryos from maternal cells in the ovule without meiosis. Many mango cultivars exhibit apomictic polyembryony, where one embryo develops from zygotic tissues and the rest from nucellar tissues, resulting in seedlings that are genetically identical to the mother tree. In Mangifera indica L. commercially important rootstocks are raised from apomictic seeds, which are then grafted with desired cultivars. Identifying molecular markers for polyembryony and understanding its genetics would facilitate introducing this trait in commercially important cultivars. In this report, genome-wide association studies were conducted on a diversity panel consisting of 42 polyembryonic and 42 monoembryonic M. indica cultivars using high-density single nucleotide polymorphism (SNP) markers. These studies revealed that the polyembryony locus is in a 360-kb region on linkage group 17 of the 'Alphonso' reference genome. This locus contains the MiRWP/MiRKD4 gene, which codes for an RWP-RK domain-containing protein previously implicated in citrus apomixis. Comparative genomic analyses revealed synteny between the citrus and the mango polyembryony loci, suggesting a common evolutionary mechanism for this trait. A total of 29 SNP markers in this locus were significantly associated with polyembryony in M. indica. Five of these markers were developed into convenient genotyping assays using competitive allele-specific PCR chemistry implemented in two different genotyping platforms - Kompetitive Allele-Specific PCR (KASP) and PCR allele competitive extension (PACE). The utility of these assays was validated and demonstrated in diverse germplasm collection and open-pollinated mango breeding populations with known pedigrees and polyembryony phenotypes. These SNP markers, especially those flanking the MiRWP/MiRKD4 gene, provide a valuable tool for mango breeders to select polyembryonic progenies at the seedling stages in mango breeding programs.

The solanaceous-infecting tobamoviruses are closely related and hence it can be challenging to detect them using serological or molecular methods, particularly when present in a mixed infection. Tomato mottle mosaic virus (ToMMV) is a newly identified tobamovirus that poses serious risk to tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.) production worldwide. Species-specific identification is crucial to prevent the entry and establishment of plant pathogens and protect the billion-dollar tomato industry. In this study, we report the validation of a previously described reverse transcription polymerase chain reaction (RT-PCR) assay that amplifies a 289 bp fragment of the coat protein coding region of ToMMV genome. This assay has 100% specificity for ToMMV. Inclusivity tests were performed against a diverse collection of six ToMMV isolates in North America. Exclusivity tests showed no cross reaction with eleven non-target viruses and seven viroids commonly found on tomato and pepper host plants. The detection limit of the one-step RT-PCR was determined to be at 10^-5 (or 0.25pg/μl) dilution in plant samples, with its amplicon sequence confirmed by Sanger sequencing. The RT-PCR can detect ToMMV consistently on contaminated seed or leaf tissues. This validated assay could serve as a standard method for detecting ToMMV in seed health testing and for plant disease diagnosis, thus to prevent inadvertent introduction and spread of this emerging and economically important tobamovirus in tomato and pepper fields.

Abies pinsapo is an endangered species, endemic to southern Spain. Somatic embryogenesis and cryopreservation constitute important biotechnological tools, which can be used in order to improve the management and conservation of threatened species. The objective of this work was to develop somatic embryogenesis and cryopreservation protocols for A. pinsapo. Somatic embryogenesis was induced from mature zygotic embryos of A. pinsapo cultured on solid MS medium with macroelements at half-strength and supplemented with 20 g L^-1 sucrose and 5 mg L^-1 6-benzylaminopurine (BA). Embryogenic cultures successfully proliferated on solid medium with the same formulation supplemented with 20 g L^-1 sucrose, 500 mg L^-1 L-glutamine, 1 g L^-1 casein hydrolysate and 1 mg L^-1 BA. Different preconditioning and cryoprotective treatments were tested in order to optimize cryopreservation of embryogenic tissues by using the slow-cooling technique. Embryogenic cultures at their exponential growth phase, i.e. 12-14 days after the last subculture, were used as cryopreservation explants. The best results were achieved after sucrose preculture and cryoprotecion with PGD I (mixture of polyethylene glycol, glucose and DMSO I), with 100% of explants resuming somatic embryogenesis after thawing. Following fluorescein diacetate (FDA) staining, more intense and abundant green fluorescence could be observed in these samples, compared to those subjected to other preconditioning and cryoprotective treatments, thus evincing a higher proportion of viable cells after freezing in liquid nitrogen. Cold hardening did not improve cryotolerance. In fact, incubation at 5 °C for two weeks appeared to affect explants response, delaying tissue regrowth after cryopreservation. This is the first time in which somatic embryogenesis and cryopreservation have been reported in Spanish fir. The results obtained allow to establish the bases for the integration of these techniques into in situ and ex situ conservation strategies.

Excessive salt accumuln in soil is one of the most important abiotic stresses in agricultural environments. The Domain of Unknown Function 868 (DUF868) family, comprising 15 members in rice, has been identified in the protein family database. In this study, we cloned and functionally characterized OsDUF868.12, a member of the OsDUF868 family, to elucidate its role in rice response to salt stress. A series of experiments, including RT-qPCR, Agrobacterium-mediated transient transformation in tobacco for localization analysis, phenotypic characterization, physiological and biochemical index measurement, and leaf staining, were conducted to investigate the function of OsDUF868.12 under salt stress. Transcriptional analysis revealed that OsDUF868.12 exhibited the most significant response to low temperature and salt stress. Preliminary subcellular localization studies indicated that OsDUF868.12 is localized in the cell membrane. Phenotypic Identification Experiments showed Overexpression lines of OsDUF868.12 enhanced resistance to salt stress and increased survival rates, while knockout lines of OsDUF868.12 were opposite. Physiological and biochemical assessments, along with leaf staining, demonstrated that overexpression of OsDUF868.12 improved the activity against oxidative stress.under salt stress. Furthermore, overexpression of OsDUF868.12 elevated the transcription levels of positively regulated salt stress-related genes. These findings suggest that overexpression of OsDUF868.12 enhances rice tolerance to salt stress at the molecular level through a series of regulatory mechanisms. This study provides valuable insights into the functional roles of the DUF868 family in plant responses to abiotic stress.

Introduction: Pollen is usually presented by the anthers after maturity. However, in some plants, pollen is presented to pollinators on other floral structures (other than the anthers), or via particular expulsion mechanisms, resulting in secondary pollen presentation. The unusual petal morphology in Berchemia mediates pollen presentation, characterised by a combination of secondary pollen presentation and primary pollen presentation. However, the function, the role in reproduction, and the evolutionary significance of the unusual petals remain unclear.

Methods: In this study, we took Berchemia flavescens and Berchemia polyphylla var. leioclada as examples, and used field observations, semi-thin sections technology, scanning electron microscopy, and pollination ecology detection methods to explore the unique pollen presentation strategies, petal functions, and reproductive strategies in Berchemia.

Results: This is a unique pollen presentation process mediated by petals. In the advanced bud stage, petals curl inward, enclosing the stamens. Following anther dehiscence, pollen is released into the petal tube, where the filament and cone-shaped anthers act as pistons, extruding pollen or pollen clumps through gaps at the petal tube apex (secondary pollen presentation). Subsequently, as the anthers emerge from the petal tube, residual pollen is directly presented to pollinators (primary pollen presentation).

Discussion: In Berchemia, the petals enclosing the stamens, effectively shield the pollen from extreme environmental conditions. The petal-stamen complex slow movement (first centrifugal, later centripetal) and pollen presentation in Berchemia suggest a unique reproductive strategy. This mechanism promotes outcrossing, minimizing interference between the pistil and stamens, and offers reproductive assurance by delayed self-pollination.

Alfalfa is one of the primary forages, and its yield is largely dependent on the development of its leaf. In this study, to elucidate the mechanism of compound leaf development, we isolated and examined the alfalfa phenotype Chuancao No.7, exhibiting five leaflets. The agronomic traits of the Chuancao No.7 including the leaf blade area, leaf/stem ratio, total fresh weight, and dry weight showed significant increases compared to those of the wild-type. Analyses of forage quality traits indicated significant differences in crude protein (CP), acid detergent fiber (ADF), crude fat (CF), water-soluble sugars (WSS), carbon content, ash composition content, and phosphorus content between Chuancao No.7 alfalfa and wild-type. Transcriptomic profile analysis revealed that differentially expressed genes were identified in the cytokinin (CK) signaling pathway. Both exogenous treatment and endogenous CK content detection indicated that cytokinin played a key role in the development of the alfalfa compound leaf. These results serve as a valuable resource for optimizing the forage quality and exploring the excellent germplasm of alfalfa.

Solanum rostratum Dunal (SrD) is a globally harmful invasive weed that has spread widely across many countries, posing a serious threat to agriculture and ecosystem security. A deep learning network model, TrackSolanum, was designed for real-time detection, location, and counting of SrD in the field. The TrackSolanmu network model comprises four modules: detection, tracking, localization, and counting. The detection module uses YOLO_EAND for SrD identification, the tracking module applies DeepSort for multi-target tracking of SrD in consecutive video frames, the localization module determines the position of the SrD through center-of-mass localization, and the counting module counts the plants using a target ID over-the-line invalidation method. The field test results show that for UAV video at a height of 2m, TrackSolanum achieved precision and recall of 0.950 and 0.970, with MOTA and IDF1 scores of 0.826 and 0.960, a counting error rate of 2.438%, and FPS of 17. For UAV video at a height of 3m, the model reached precision and recall of 0.846 and 0.934, MOTA and IDF1 scores of 0.708 and 0.888, a counting error rate of 4.634%, and FPS of 79. Thus, the TrackSolanum supports real-time SrD detection, offering crucial technical support for hazard assessment and precise management of SrD.

The avocado industry faces a significant threat from the hemibiotrophic oomycete pathogen Phytophthora cinnamomi. A variably expressed defence gene during an avocado infection trial was a Wall-associated kinase (WAK). WAK and WAK-Like (WAKL) proteins are known to bind to fragmented pectin (oligogalacturonides) produced during pathogen penetration, thereby activating downstream defence-related pathways. To better understand the P. cinnamomi-avocado defence interaction, this gene family was assessed using in silico methods. In this study, previously generated RNA-sequencing data were used to associate genes with the defence response, followed by promoter- and phylogenetic analysis of these genes/proteins. The predicted proteins from these genes were modelled with AlphaFold2, and structural similarity across different rootstocks, as well as their binding affinity for oligogalacturonides, were assessed. The analysis identified 14 Persea americana (Pa)WAKs and 62 PaWAKLs across the West-Indian (pure accession reference), Dusa^®, Leola™ and R0.12 avocado rootstock genomes. These genes showed distribution across the West-Indian genome's chromosomes, with MCScanX analyses predicting tandem duplications. PaWAK/WAKL expression profiles were compared, implicating five PaWAK/WAKLs in defence. Phylogenetic and promoter analyses were conducted to predict associated defence-related pathways, focusing on stress and phytohormone-responsive pathways. Structural differences and varying oligogalacturonide binding affinities of PaWAK/WAKLs were predicted across rootstocks. These defence-related genes could be incorporated into a molecular screening tool to improve the development of resistant avocado rootstocks.