Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), represents a significant threat to the global citrus industry. LATERAL ORGAN BOUNDARIES 1 (LOB1) has been identified as a key gene involved in the development of citrus canker in susceptible varieties. However, the role and molecular mechanisms of LOB1 in disease-resistant varieties, such as Kumquat (Fortunella spp.), remain poorly understood. In this study, transgenic kumquat plants with either Citrus sinensis LOB1 (CsLOB1) overexpression or RNAi-mediated silencing were obtained to investigate the function and molecular basis of LOB1 in kumquat resistance to Xcc. Overexpression of CsLOB1 in kumquats resulted in dwarf phenotype with reduced leaf size, increased branching, and numerous pustule-like bulges resembling citrus canker. Microscopic analysis revealed that these bulges were due to the excessive proliferation of mesophyll cells, along with spongy cell enlargement and palisade cell shortening. Resistance assays showed that CsLOB1 overexpression promoted kumquat susceptibility to Xcc, while the resistance remained stable in the RNAi lines. RNA-seq analysis revealed that CsLOB1 significantly upregulated immune response-related genes in kumquat. Furthermore, CsLOB1 was shown to regulate kumquat immunity through modulation of indole- 3-acetic acid-amido synthetase 3.17 (GH3.17), elongation factor tu receptor (EFR), mitogen-activated protein kinase kinase 5 (MKK5) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1). Taken together, these findings demonstrate that CsLOB1 not only promotes citrus canker development by altering cellular states and hormone signaling but also activates immune responses in kumquat. Our work offers insights into harnessing LOB1 in the breeding of canker-resistant varieties in citrus.

The SQUAMOUS PROMOTER BINDING PROTEIN-LIKE (SPL) gene family encodes plant-specific transcription factors that regulate diverse physiological processes, including growth, flowering, and stress responses. A total of 32 PaSPL genes were identified and characterized in the genome of Platanus × acerifolia, an ancient hexaploid species widely cultivated as a street tree. The PaSPL genes were classified into nine distinct groups based on their phylogenetic relationship. Gene structure examination revealed considerable variation in intron number and length among groups. Cis-regulatory element analysis indicated that the promoter regions of PaSPLs are enriched with light-responsive elements. Expression profiling across different tissues and developmental stages demonstrated that the PaSPL genes harboring a site targeted by microRNA156 exhibited stage-specific expression patterns, while those in the Groups II, III, V, and IX displayed tissue-specific expression. Notably, several PaSPL genes exhibited dynamic expression during floral transition, implicating their role in flowering regulation. Among them, PaSPL8a, a Group III member, was differentially expressed in flowerless germplasm resources. Functional characterization demonstrated that PaSPL8a overexpression in Arabidopsis thaliana accelerated flowering and upregulated key flowering regulators. These findings provide mechanistic insights into the function of PaSPLs in P. × acerifolia and establish PaSPL8a as a positive regulator of flowering.

Late blight, caused by Phytophthora infestans, is one of the most devastative global plant threats. Pyramiding multiple resistance genes (R genes) was initially considered as a promising strategy for breeding broad-spectrum late blight-resistance potato varieties. However, stacking multiple R genes may induce detrimental effects on plant health. Fine-tuning the expression of R genes is critical for their effective stacking in potato breeding. This study confirms that low-level expression of individual potato late blight resistance genes like RB, R8, and Vnt1.1, controlled by the CaMV 35S promoter, does not trigger cell death (CD). However, co-expression of these genes in Nicotiana benthamiana leaves induces CD. Plant upstream open reading frames (uORFs) attenuate the translation of the downstream main ORF. We demonstrates that N. benthamiana open reading frame (NbuORF) and Solanumtuberosum L. open reading frame (StuORF) completely suppress green fluorescent protein (GFP) translation, whereas Arabidopsisthaliana open reading frames (AtuORFs) only partially inhibit GFP translation in N. benthamiana leaves. Simultaneous expression of AtuORFs or StuORF and RB, under the control of either pathogen-inducible potato vetispiradiene synthase gene 3 (PVS3) promoter or the 35S promoter, leads to inhibition of CD. Transgenic potatoes with 35S::RB exhibit superior late blight resistance compared to PVS3::RB transgenic lines. Plants expressing 35S::StuORF-RB show increased resistance, although slightly lower than that of 35S::RB transgenic plants. However, 35S::AtuORFs-RB and PVS3::AtuORFs-RB transgenic potatoes are susceptible to P. infestans, suggesting that AtuORFs and StuORF suppress RB translation in these plants. These findings highlight the potential of different promoter and uORF combinations for finely tuning R gene expression, which may optimize the balance between plant resistance and normal growth.

Pathogenesis-related proteins (PRs) are essential for plant defense against both biotic and abiotic stresses. However, knowledge regarding PRs in pears remains limited. In this study, 637 PRs, classified into 16 families, were identified in Pyrus bretschneideri. Phylogenetic, sequence similarity, and secondary structure analyses enabled the classification of several PRs with conserved sequences, including PR-11, PR-8, PR-15, and PR-16. Genomic analysis revealed that the expansion of most PR families resulted from recent whole-genome duplication (WGD) events, occurring approximately 30–45 million years ago (Mya). Various gene duplication mechanisms have collectively contributed to the proliferation of PR families, with purifying selection indicated by the low Ka/Ks ratios. Examination of apoplastic fluid composition showed that only a subset of PRs was present in the apoplast. Transcriptomic data from Pyrus infected with Erwinia amylovora and Colletotrichum fructicola revealed the expression profiles of PR genes post-infection, underscoring the complexity of PR regulation. This study elucidates the evolutionary expansion, regulation, and functional roles of PRs in disease resistance, highlighting certain PRs as reliable markers of pear disease resistance. These findings offer valuable insights for future functional analyses and breeding strategies to enhance pear resistance to pathogens.

Model organisms have been instrumental in advancing discoveries in plant biology. Tomato (Solanum lycopersicum) is distinguished as a prominent model system due to its well-characterized genetics and economic significance as a crop. Micro-Tom (MT), an ornamental dwarf tomato variety, was adopted by the tomato research community as a model plant due to its short stature, fast life cycle, ease of genetic transformation, and ample genomic resources. Over the last 30 years, the use of MT has illuminated various facets of plant development, including the control of growth habit, glandular trichomes, leaf anatomy, and the formation of arbuscular mycorrhizal symbioses. We briefly summarize these contributions and point to further potential advances in the future.

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), poses a significant threat to the kiwifruit industry. Certain kiwifruit species, such as Eri-1 (Actinidia eriantha), exhibit resistance to Psa, as indicated by the minimal symptoms observed on their shoots and canes. However, discrepancies between leaf disease symptoms and resistance levels have been noted, and the underlying mechanisms remain poorly understood. This study explored the distinctive responses of Psa-resistant Eri-1 leaves to Psa infection. Upon inoculation, Eri-1 leaves activated protein kinase genes associated with pattern-triggered immunity (PTI), induced stomatal closure, and subsequently triggered resistance genes involved in effector-triggered immunity (ETI). However, suppression of downstream hypersensitive response (HR) signaling pathways in both PTI and ETI was observed, limiting reactive oxygen species (ROS) production and programmed cell death (PCD), thus impairing pathogen elimination. Additionally, upon Psa inoculation, the Psa-resistant Eri-1 predominantly activated lignin biosynthesis genes, while the Psa-susceptible ‘Hongyang’ activated flavonol biosynthesis genes within the shared phenylpropanoid pathway. This differential response mechanism facilitates Psa containment in Eri-1 leaves by promoting lignin accumulation, ultimately leading to pathogen elimination. These findings deepen our understanding of plant-pathogen interactions, providing insights into Psa pathogenesis and kiwifruit resistance, and offering valuable guidance for early-stage prevention and control strategies to mitigate crop losses.

Plant dwarfing is a key agronomic trait, often characterized by shortened internodes and increased branching and leaf production, which improves lodging resistance and facilitates intensive crop planting. In fruit crops, dwarfing promotes dense planting, enhancing land utilization and simultaneously boosting fruit yield and quality, thus driving higher economic returns with reduced labor costs. Significant advancements have been made in elucidating the mechanisms underlying fruit tree dwarfing despite their complex genetic backgrounds, largely due to the rapid progress in modern molecular technologies. This article reviews the morphological and physiological features of dwarfing in fruit trees and examines the molecular regulatory mechanisms, with a particular focus on plant hormones such as gibberellins, auxins, brassinosteroids, and abscisic acid. Furthermore, this review highlights future research directions, including the identification of hormone-related dwarfing determinants, the dissection of comprehensive molecular regulatory networks using cutting-edge techniques like single-cell sequencing, high-resolution microscopy, in situ imaging, and multi-omics approaches. These new insights into fruit tree dwarfing lay a solid foundation for a deeper understanding of plant growth regulation in a new era, offering promising avenues for controlling plant growth through manipulation of key factors, especially hormones, or for the development of new cultivars or rootstocks with stable dwarf phenotypes via molecular breeding, ultimately advancing fruit productivity in the future.

Pears rank as the third most produced fruit in China, with widespread cultivation throughout the country. Asexual propagation, primarily through grafting onto Pyrus betulifolia rootstocks, is the predominant method of cultivation. However, the absence of an efficient genetic transformation system for P. betulifolia significantly hinders genetic enhancement efforts for pear rootstocks. In this study, TDL39, a P. betulifolia genotype, was identified for its remarkable regenerative capacity. Leaf strips derived from 60-day-old TDL39 seedlings were cultured abaxial side up on a regeneration medium consisting of NN69, 3.0 mg/L thidiazuron (TDZ), 0.1 mg/L indole-3-butyric acid (IBA), 30 g/L sucrose, and 6.6 g/L agar. The strips were kept in the dark for 28 days and subsequently exposed to light for 30 days, resulting in the formation of adventitious shoots with an average regeneration rate of 81.5%. Employing this regeneration protocol, transgenic P. betulifolia plants overexpressing the Green Fluorescent Protein (GFP) gene were successfully generated, with 15 mg/L kanamycin (Kan) used for selection. The highest transformation efficiency achieved was 4.2%. This study successfully establishes a regeneration system for P. betulifolia and facilitates the production of transgenic plants, thereby advancing molecular breeding and the functional characterization of P. betulifolia and other pear genotypes.

Plant growth-promoting rhizobacteria (PGPR) enhance nutrient accessibility and offer disease protection, conferring significant advantages to host plants. Although considerable progress has been made in PGPR research, efficient acquisition of PGPR remains challenging, primarily due to the absence of a microbial biobank, especially for perennial woody crops like citrus. Through 16S rRNA amplicon sequencing, this study analyzed rhizobacterial communities from five citrus-producing regions in China, identifying 9,887 amplicon sequence variants (ASVs) across 28 rhizobacterial phyla. Subsequently, a citrus rhizosphere microbial biobank was established, comprising 3,142 bacterial strains, through extensive isolation of citrus rhizobacteria. From this collection, 269 potential PGPR were screened from 435 bacterial taxa based on their production of indole-3-acetic acid (IAA), siderophore synthesis, phosphate solubilization, and their effects on Arabidopsis root growth. Further evaluation of 22 selected PGPR strains via pot-culture inoculation on citrus and tomato seedlings demonstrated that 11 strains significantly enhanced plant growth. This study provides a foundational theoretical and technological framework for advancing the development and application of beneficial rhizobacteria in citrus agriculture.