Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice bacterial blight disease, which causes a large reduction in rice production. The successful interaction of pathogens and plants requires a particular nutrient environment that allows pathogen growth and the initiation of both pathogen and host responses. Amino acid synthesis is essential for bacterial growth when bacteria encounter amino acid-deficient environments, but the effects of amino acid synthesis on Xoo pathogenicity are unclear. Here, we systemically deleted the essential genes (leuB, leuC, leuD, ilvC, thrC, hisD, trpC, argH, metB, and aspC) involved in the synthesis of different amino acids and analyzed the effects of these mutations on Xoo virulence. Our results showed that leucine, isoleucine, valine, histidine, threonine, arginine, tryptophan, and cysteine syntheses are essential to Xoo infection. We further studied the role of leucine in the interaction between pathogens and hosts and found that leucine could stimulate some virulence-related responses and regulate Xoo pathogenicity. Our findings highlight that amino acids not only act as nutrients for bacterial growth but also play essential roles in the Xoo and rice interaction.

Xanthomonas campestris pv. campestris (Xcc) can cause black rot in cruciferous plants worldwide. Two‐component systems (TCSs) are key for bacterial adaptation to various environments, including hosts. VemR is a TCS response regulator and crucial for Xcc motility and virulence. Here, we report that RavA is the cognate histidine kinase (HK) of VemR and elucidate the signalling pathway by which VemR regulates Xcc motility and virulence. Genetic analysis showed that VemR is epistatic to RavA. Using bacterial two‐hybrid experiments and pull‐down and phosphorylation assays, we found that RavA can interact with and phosphorylate VemR, suggesting that RavA is the cognate HK of VemR. In addition, we found that RpoN2 and FleQ are epistatic to VemR in regulating bacterial motility and virulence. In vivo and in vitro experiments demonstrated that VemR interacts with FleQ but not with RpoN2. RavA/VemR regulates the expression of the flagellin‐encoding gene fliC by activating the transcription of the rpoN2‐vemR‐fleQ and flhF ‐ fleN ‐ fliA operons. In summary, our data show that the RavA/VemR TCS regulates FleQ activity and thus influences the expression of motility‐related genes, thereby affecting Xcc motility and virulence. The identification of this novel signalling pathway will deepen our understanding of Xcc–plant interactions.

Identification of genes involved in mangrove species’ adaptation to salt stress can provide valuable information for developing salt-tolerant crops and understanding the molecular evolution of salt tolerance in halophiles. Ceriops tagal is a salt-tolerant mangrove tree growing in mudflats and marshes in tropical and subtropical areas, without any prior genome information. In this study, we assessed the biochemical and transcriptional responses of C. tagal to high salt treatment (500 mmol/L NaCl) by hydroponic experiments and RNA-seq. In C. tagal root tissues under salt stress, proline accumulated strongly from 3 to 12 h of treatment; meanwhile, malondialdehyde content progressively increased from 0 to 9 h, then dropped to lower than control levels by 24 h. These implied that C. tagal plants could survive salt stress through biochemical modification. Using the Illumina sequencing platform, approximately 27.39 million RNA-seq reads were obtained from three salt-treated and control (untreated) root samples. These reads were assembled into 47,111 transcripts with an average length of 514 bp and an N50 of 632 bp. Approximately 78% of the transcripts were annotated, and a total of 437 genes were putative transcription factors. Digital gene expression analysis was conducted by comparing transcripts from the untreated control to the three salt treated samples, and 7,330 differentially expressed transcripts were identified. Using k-means clustering, these transcripts were divided into six clusters that differed in their expression patterns across four treatment time points. The genes identified as being up- or downregulated are involved in salt stress responses, signal transduction, and DNA repair. Our study shows the main adaptive pathway of C. tagal in saline environments, under short-term and long-term treatments of salt stress. This provides vital clues as to which genes may be candidates for breeding salt-tolerant crops and clarifying molecular mechanisms of salt tolerance in C. tagal. The expression levels of 20 candidate genes measured by RNA-Seq were validated via qRT-PCR. Eighteen genes showed consistent expression patterns in RNA-Seq and qRT-PCR results, suggesting that the RNA-seq dataset was dependable for gene expression pattern analysis.

Cassava (Manihot esculenta Crantz) is a staple crop in tropical and subtropical regions, valued for its high starch content in roots. Effective genetic transformation and genome editing of cassava require efficient screening methods for transgenic and edited plants. In this study, a visual selection marker system using an R2R3-MYB transcription factor anthocyanin 1 gene (HbAN1, LOC110667474) from a rubber tree (Hevea brasiliensis Müll. Arg.) has been developed to facilitate the identification of transgenic cassava plants. Transgenic cassava lines expressing HbAN1 accumulated anthocyanins in their leaves, allowing for easy visual identification without the need for destructive assays or specialized equipment. Importantly, the accumulation of anthocyanins did not affect the regeneration or transformation efficiency of cassava. Additionally, the AR-CRISPR/Cas9-gRNA system with the HbAN1 gene as a marker produced MeCDD4 gene-edited cassava mutants with purple leaves, demonstrating successful editing. This anthocyanin-based visual reporter (AR) system will provide an effective tool for genetic transformation and genome editing in cassava.

Riboswitches are RNA elements that sense metabolites and control gene expression. Recently, the yybP-ykoY riboswitches were found to sense manganese (Mn²⁺) and regulate the expression of diverse genes. Here, we show that the leader RNA (a yybP-ykoY RNA) of yebN in Xanthomonas oryzae pv. oryzae also functions as a sensor of Mn²⁺. This leader RNA detects Mn²⁺ levels in plants and is essential to X. oryzae pv. oryzae virulence. Our data also indicate that Mn²⁺ is not only required as a microelement for plant growth but also acts as a defense molecule to inhibit pathogen growth. This finding highlights that Mn²⁺ plays important roles in pathogen-plant interactions and that the yebN leader RNA can be a target candidate for anti–X. oryzae pv. oryzae drug development.