Molecular Horticulture最新文献

Citrus bacterial canker (CBC), caused by Xanthomonas citri subsp. citri (Xcc), poses a significant threat to the citrus industry. Xcc employs the transcription activator-like effector (TALE) PthA4 to target the major susceptibility (S) gene CsLOB1 in citrus, promoting host susceptibility to bacterial canker. However, the contribution of other Xcc TALEs, aside from PthA4, to virulence remains underexplored. In this study, we characterized two PthA1 variants, designated PthA5 and PthA6, which facilitate Xcc infection in susceptible citrus species by promoting the formation of hypertrophy and hyperplasia symptoms. Both PthA5 and PthA6 bind directly to effector-binding elements (EBEs) in the promoter of CsGRAS9, suppressing its expression. CsGRAS9 negatively regulates Xcc growth in citrus and contributes to CBC resistance. Notably, natural variations in the EBEs of the FhGRAS9 promoter, a homolog of CsGRAS9 in Hong Kong kumquat, prevent Xcc from affecting FhGRAS9 expression. Using the PTG/Cas9 system, we generated proCsGRAS9-edited sweet orange lines #18-2 and #23, which contain 86-bp and 62-bp deletions in the EBE regions of the CsGRAS9 promoter. These mutant lines showed enhanced CsGRAS9 expression and increased resistance to CBC during Xcc infection. Several GA-related genes and CsTAC1, regulated by CsGRAS9, were also identified. This is the first report that TALEs act as repressors of a resistance gene to confer host susceptibility.

The rapid development of Prunus pseudocerasus related industry has increasingly contributed to rural vitalization in China. This study employed a biomod2 ensemble model, utilizing environmental and species occurrence data from 151 P. pseudocerasus germplasm wild/local samples, to predict potential geographical distribution, suitability changes, climate dependence, and ecological niche dynamics. The optimized maximum entropy (MaxEnt) model yielded the most accurate predictions. The climate variables with the greatest impact on suitability were precipitation of warmest quarter and mean diurnal temperature range. The total potential suitable area for P. pseudocerasus was approximately 2.78 × 10⁶ km², increasing with CO₂ concentration. The highly suitable area was primarily concentrated in basin terrains, plateaus, and plains of Sichuan Province. The current centroid in Lichuan exhibited gradual latitudinal and longitudinal movement. The predicted (2090s) ecological niche trends of P. pseudocerasus varied under different pathways and periods, with higher CO₂ concentration associated with lower niche overlap. The CO₂ emission concentration in the SSP246 scenario emerged as the most suitable climate model. Climate change is driving both the expansion of geographical distribution and the contraction of overlapping geographical distribution areas of P. pseudocerasus. These findings provide a theoretical basis for wild resource conservation, site selection for production, and introduction of allopatry for P. pseudocerasus.

Powdery mildew (PM), caused by the biotrophic fungus Podospharea leucotricha, poses a significant threat to apple production. Salicylic acid (SA) signaling plays a crucial role in enhancing resistance to biotrophic pathogens. While PR1, a defense protein induced by SA, is essential for plant immunity, its excessive accumulation can be detrimental. However, the mechanism of PR1-mediated immune balance remains unclear. This study identified a key transcription factor, WRKY1, which enhances the SA accumulation by modulating the SA biosynthesis gene EPS1, while simultaneously regulating the WRKY40-NPR3g module to prevent sustained PR1 expression caused by continuous SA accumulation. Specifically, the transcription factor WRKY40 upregulates NPR3g expression, and NPR3g interacts with NPR1 in an SA-dependent manner. Then, two TGA2c variants that interact with NPR1 to activate PR1 expression were identified: canonical TGA2c-1 and alternative splicing of TGA2c-2 with an exon deletion. SA does not influence the NPR1-TGA2c-1 interaction but is essential for the NPR1-TGA2c-2 interaction. Notably, NPR3g reduces PR1 levels by selectively disrupting the NPR1-TGA2c-2 complex through competition for the BTB-POZ domain of NPR1. In conclusion, this study identifies a novel mechanism by which WRKY1 modulates PR1-mediated immune balance to defend against PM.

Dynamic DNA methylation represses transposable elements (TEs) and regulates gene activity, playing a pivotal role in plant development. Although substantial progress has been made in understanding DNA methylation reprogramming during germline development in Arabidopsis thaliana, whether similar mechanisms exist in other dicot plants remains unclear. Here, we analyzed DNA methylation levels in meiocytes, microspores, and pollens of Brassica Rapa using whole-genome bisulfite sequencing (WGBS). Global DNA methylation analysis revealed similar CHH methylation reprogramming compared to Arabidopsis, while distinct patterns were observed in the dynamics of global CG and CHG methylation in B. rapa. Differentially methylated region (DMR) analysis identified specifically methylated loci in the male sex cells of B. Rapa with a stronger tendency to target genes, similar to observations in Arabidopsis. Additionally, we found that the activity and genomic targeting preference of the small RNA-directed DNA methylation (RdDM) were altered during B. Rapa male germline development. A subset of long terminal repeat (LTR) TEs were activated, possibly due to the dynamic regulation of DNA methylation during male sexual development in B. Rapa. These findings provided new insights into the evolution of epigenetic reprogramming mechanisms in plants.

The role of ethylene as an initial signaling molecule in waterlogging stress is well-established. However, the complex molecular mechanisms underlying ethylene biosynthesis and its functional significance in chrysanthemums under waterlogging conditions have remained unclear. In this study, we observed an increase in the expression of 1-aminocyclopropane-1-carboxylate synthase 6 (CmACS6), which encodes a key enzyme responsible for ethylene biosynthesis, in response to waterlogging. This elevation increases ethylene production, induces leaf chlorosis, and enhances the chrysanthemum's sensitivity to waterlogging stress. Moreover, our analysis of upstream regulators revealed that the expression of CmACS6, in response to waterlogging, is directly upregulated by CmHRE2-like (Hypoxia Responsive ERF-like, CmHRE2L), an ethylene response factor. Notably, CmHRE2-L binds directly to the GCC-like motif in the promoter region of CmACS6. Genetic validation assays demonstrated that CmHRE2L was induced by waterlogging and contributed to ethylene production, consequently reducing waterlogging tolerance in a partially CmACS6-dependent manner. This study identified the regulatory module involving CmHRE2L and CmACS6, which governs ethylene biosynthesis in response to waterlogging stress.

Cold stress adversely affects crop growth and development. Radish is an important root vegetable crop, and its taproot formation is susceptible to low temperatures. However, the molecular basis of the cold stress response has not yet been fully dissected in radish. Here, a sucrose phosphate synthase gene (RsSPS1) was identified through a genome-wide association study and transcriptome analysis. RsSPS1 was responsible for sucrose synthesis, and sucrose was shown to be involved in taproot growth, cambium activity, and cold tolerance in radish. RsSPS1 regulated cambium activity and cold stress response by modulating sucrose content. Moreover, RsWRKY40 was identified as the upstream transcription activator of RsSPS1 by binding to its promoter. RsWRKY40 functioned in cambium activity and cold tolerance by modulating RsSPS1-mediated sucrose accumulation. Furthermore, RsWRKY40 promoted the RsCBF1 and RsCBF2 expression levels, resulting in elevated cold resilience. RsWRKY40 also enhanced its own transcription, forming a positive auto-regulatory loop to regulate cold stress response in radish. Together, a transcription module of RsWRKY40 orchestrated cold stress response by integrating sucrose accumulation and the CBF-dependent pathway was uncovered. These findings would provide novel insight into the molecular mechanism underlying cold-responsive sucrose accumulation and cambium activity and facilitate the genetic improvement of cold tolerance in radish breeding programs.

The S-RNase-based self-incompatibility locus (S-locus) in Petunia species contains 16-20 F-box genes, which collaboratively function in the recognition and subsequent degradation of non-self S-RNases, while distinguishing them from self S-RNase. However, the number of S-locus F-box genes (SFBBs) physically interacted with non-self S-RNases remains uncertain in Pyrus species. Utilizing Pacbio long-read sequencing, we successfully assembled the genome of pear cultivar 'Yali' (Pyrus bretschneideri), and identified 19 SFBBs from the Pyrus S₁₇-locus spanning approximately 1.78 Mb. Additionally, we identified 17-21 SFBBs from other Pyrus and Malus S-loci spanning a range of 1.35 to 2.64 Mb. Based on the phylogenetic analysis, it was determined that Pyrus and Malus SFBBs could be classified into 22 groups, denoted as I to XXII. At amino acid level, SFBBs within a given group exhibited average identities ranged from 88.9% to 97.9%. Notably, all 19 SFBBs from the S₁₇-locus co-segregated with S₁₇-RNase, with 18 of them being specifically expressed in pollen. Consequently, these 18 pollen-specifically expressed SFBBs are considered potential candidates for the pollen-S determinant. Intriguingly, out of the 18 pollen-specifically expressed SFBBs, eight demonstrated interactions with at least one non-self S-RNase, while the remaining SFBBs failed to recognize any S-RNase. These findings provide compelling evidence supporting the existence of a collaborative non-self-recognition system governing self-incompatibility in pear species.