The soilborne pathogen Ralstonia solanacearum is the causal agent of bacterial wilt (BW), a major disease of pepper (Capsicum annuum). The genetic basis of resistance to this disease in pepper is not well known. This study aimed to identify BW resistance markers in pepper. Analysis of the dynamics of bioluminescent R. solanacearum colonization in reciprocal grafts of a resistant (BVRC 1) line and a susceptible (BVRC 25) line revealed that the resistant rootstock effectively suppressed the spreading of bacteria into the scion. The two clear-cut phenotypic distributions of the disease severity index in 440 F2 plants derived from BVRC 25 × BVRC 1 indicated that a major genetic factor as well as a few minor factors that control BW resistance. By specific-locus amplified fragment sequencing combined with bulked segregant analysis, two adjacent resistance-associated regions on chromosome 10 were identified. Quantitative trait (QTL) mapping revealed that these two regions belong to a single QTL, qRRs-10.1. The marker ID10-194305124, which reached a maximum log-likelihood value at 9.79 and accounted for 19.01% of the phenotypic variation, was located the closest to the QTL peak. A cluster of five predicted R genes and three defense-related genes, which are located in close proximity to the significant markers ID10-194305124 or ID10-196208712, are important candidate genes that may confer BW resistance in pepper.

Watermelon is one of the most important cucurbit crops, but its production is seriously affected by viral infections. Although eIF4E proteins have emerged as the major mediators of the resistance to viral infections, the mechanism underlying the contributions of eIF4E to watermelon disease resistance remains unclear. In this study, three CleIF4E genes and one CleIF(iso)4E gene were identified in the watermelon genome. Among these genes, CleIF4E1 was most similar to other known eIF4E genes. To investigate the role of CleIF4E1, CRISPR/Cas9 technology was used to knock out CleIF4E1 in watermelon. One selected mutant line had an 86 bp deletion that resulted in a frame-shift and the expression of a truncated protein. The homozygous mutant exhibits developmental defects in plant growth, leaf morphology and reduced yield. Furthermore, the mutant was protected against the zucchini yellow mosaic virus, but not the cucumber green mottled mosaic virus. In summary, this study preliminarily clarified the functions of eIF4E proteins in watermelon. The generated data will be useful for elucidating eIF4E-related disease resistance mechanisms in watermelon. The tissue-specific editing of CleIF4E1 in future studies may help to prevent adverse changes to watermelon fertility.

Squash leaf curl China virus (SLCCNV) is a species in the genus Begomovirus that possess a bipartite genome. It is transmitted by the whitefly species Bemisia tabaci and infects cucurbit crops in various parts of the Old World (Wu et al., 2020). In 2020, tomato plants with curled, distorted and yellow leaves were found in a greenhouse in Shouguang, Shandong Province, China (Fig. S1). Leaves with these symptoms were collected from 11 plants and the total RNA was extracted with TRIzol reagent (Invitrogen, USA). Five RNA extracts of the highest quality were combined and a small RNA library was generated by the company (BGI-Shenzhen, China). About 22,338,920 clean reads (18-28nt) were acquired and assembled into larger contigs with the software Velvet 1.0.5. These were further compared against nucleotide sequences in the National Center for Biotechnology Information (NCBI) databases with BLASTn searches. Not unexpectedly, there were many assembled contigs that had high identities (90%-100% identities) with known tomato-infecting viruses, including 241 contigs matching tomato chlorosis virus, 26 contigs matching southern tomato virus, and 4 contigs matching tomato yellow leaf curl virus. However, 12 contigs had high identities (90%-100%) with the genomic DNA-A of SLCCNV, while 9 other contigs had high identities (90%-100%) with the genomic DNA-B of SLCCNV. To verify the presence of SLCCNV in tomato plants, two sets of primer pairs were designed according to the specific contigs assembled from derived small interfering RNAs (vsiRNAs). The primer pairs A742-F/A742-R (5'-GTAATACGAGCATCCGCACGGTAG-3'/5'-CGTGGAGGGCGAC AAACAGCTAACG-3') and B539-F/B539-R (5'-GCTACTTTCAAGGACGAAGAAGAGG-3'/5'-CG ACATAGATTTCTGGTCGGTGGGC-3') directed the amplification of 742 bp and 539 bp for DNA-A and DNA-B fragments, respectively, from the total genomic DNA of the 11 tomato samples. The DNA-A and DNA-B of SLCCNV were both detected from all of the tomato samples. After sequencing, the 742 bp PCR products shared 100% nucleotide sequence identity with the DNA-A of SLCCNV isolate GDXW (MW389919), whereas the PCR-amplified 539 bp fragments shared 100% nucleotide sequence identity with the DNA-B of SLCCNV isolate GDXW (MW389920). The full-length of DNA-A and DNA-B components were amplified with back-to-back primers A-F/A-R (Wu et al., 2020) and B-F/B-R (5'-GATAAACACGTCTCATTGCACCGC-3'/5'-GAGACGTGTTTATCAATATGGA CG-3'), respectively. The amplified fragments were further cloned into the PCE2TA/Blunt-Zero vector (Vazyme Biotech Co., China). After sequencing, the complete sequence of DNA-A was 2736 nt in length (MZ682117), while the DNA-B was 2718 nt in length (OK236348). The phylogenetic relationships of the DNA-A and DNA-B components were determined using MEGA 7 based on the full-length sequences of DNA-A and DNA-B, respectively (Kumar et al., 2016). Results showed that the DNA-A formed an independent cluster and was mostly related to the GDHY (MW389917) in the phylogenetic tree constructed using the neighbor-joining (NJ) method, while the DNA-B formed an independent cluster and was mostly related to the SLCCNV isolate BLDG (MW389928) and isolate GDBL (MW389922) (Fig. S2). The nt identities of DNA-A were also calculated with SDT v1.2 by comparison with other begomovirus sequences from the initial BLASTn analysis (Muhire et al., 2014), showing that the virus shared 99.4% sequence identity with SLCCNV isolate GDHY (MW389917). According to the current demarcation threshold for begomoviruses, recommended by the International Committee on Taxonomy of Viruses (ICTV) (91% nt identity) (Brown et al., 2015), this virus identified from tomato is a distinct strain of SLCCNV, designated SLCCNV-SDSG. To the best of our knowledge, this is the first report of a natural infection of SLCCNV on tomato in China. SLCCNV has caused serious problems in cucurbit production in some areas, so it will be important to investigate if tomato plays a role in the disease biology by serving as a reservoir host. The author(s) declare no conflict of interest. Funding: The funding for this research was supported by the Beijing Academy of Agriculture and Forestry Foundation, China (QNJJ202131, QNJJ201915, KJCX20200113). References: Brown et al. 2015. Arch Virol 160: 1593-1619 Kumar et al. 2016. Mol Biol Evol, 33: 1870-1874 Muhire et al. 2014. Plos One, 9 Wu et al. 2020. J Integr Agr, 19: 570-577.

Karrikins (KARs), produced during wildfires, are bioactive compounds that stimulate seed germination in fire-prone ecosystems and influence broader plant–environment interactions. These compounds act through the α/β hydrolase receptor KARRIKIN INSENSITIVE2 (KAI2), which perceives KARs as analogs of the hypothesized phytohormone KAI2 ligand (KL). KAR signaling shares molecular parallels with strigolactones (SLs), another class of butenolide plant hormones, and regulates diverse processes such as seedling development, root architecture, photomorphogenesis, and stress responses. Despite its multifaceted roles, the mechanistic basis of KAR-mediated regulation remains poorly understood. This review synthesizes insights into KAR signaling mechanisms, emphasizing recent advances in signal transduction pathways and functional studies. It also addresses key unresolved questions, including the identity of endogenous KL and the crosstalk between KARs and other hormonal networks. By elucidating these mechanisms, KAR-based strategies hold promises for enhancing crop resilience and sustainability, offering novel avenues for agricultural innovation in changing environments.