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Comprehensively controlling phytoplasma-associated jujube witches' broom (JWB) disease is extremely challenging for the jujube industry. Although the pathogenesis of phytoplasma disease has been highlighted in many plant species, the release of lateral buds from dormancy under JWB phytoplasma infection has not been characterized in woody perennial jujube. Here, two 16SrV-B group phytoplasma effectors, SJP1 and SJP2, were experimentally determined to induce witches' broom with increased lateral branches. In vivo interaction and subcellular localization analyses showed that both SJP1 and SJP2 were translocated from the cytoplasm to the nucleus to target the CYC/TB1-TCP transcription factor ZjBRC1. The N- and C-terminal coiled-coil domains of SJP1 and SJP2 were required for the TCP-binding ability. ZjBRC1 bound directly to the auxin efflux carrier ZjPIN1c/3 promoters and down-regulated their expression to promote the accumulation of endogenous auxin indole-3-acetic acid in jujube calli. Furthermore, JWB phytoplasma infection suppressed ZjBRC1 accumulation and induced ZjPIN1c/3 expression to stimulate lateral bud outgrowth. Therefore, SJP1 and SJP2 stimulate lateral bud outgrowth, at least partly, by repressing the ZjBRC1-controlled auxin efflux channel in jujube, representing a potential strategy for comprehensive phytoplasma-associated disease control and a resource for gene editing breeding to create new cultivars with varying degrees of shoot branching.

Jujube witches’ broom (JWB), associated with ‘Candidatus Phytoplasma ziziphi’, is a devastating disease in Chinese jujube (Ziziphus jujuba Mill.). One of the symptoms in plants infected with phytoplasmas is the change of floral organs into leaf-like structures, known as phyllody. Effector proteins secreted by phytoplasmas are key to inducing this and other witches’ broom symptoms. However, the phytoplasma effector proteins that induce phyllody in jujube remain unknown. We identified 43 candidate secreted JWB phytoplasma proteins (SJPs) in the JWB phytoplasma genome. Eight of the predicted candidate effector genes exhibited high transcript levels in infected flower buds. Among the eight candidate effectors, SJP3 experimentally showed the potential to induce phyllody. SJP3 expression in infected jujube was at a high level in young leaves and flowers. Ectopic expression of SJP3 in Arabidopsis induced leaf-like flowers and extra secondary flowers and significantly changed the transcript levels of PISTILLATA (PI), SHORT VEGETATIVE PHASE (SVP), AGAMOUS-LIKE 24 (AGL24) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). The expression levels of these MADS-box homologous genes were also changed in infected jujube flower buds and all four whorls of the floral organs. The data showed that the effector SJP3 disrupts expression of several MADS-box genes associated with floral organ identity and flowering time and is likely key to inducing phyllody in phytoplasma-infected jujube. This study provides new insight into understanding the pathogenesis of JWB disease induced by phytoplasma.

The performance of the geopolymer synthesized using red mud and coal metakaolin when exposed to sulfuric acid solutions was evaluated. The effects of different soaking times on mechanical properties, electrochemical properties, and microstructural changes to the materials were investigated. The degradation of the geopolymer was studied using corrosion depth and weight testing, uniaxial compression test, electrochemical impedance spectroscopy (EIS), nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), and scanning electron microscope-energy dispersive spectrometry (SEM-EDS). The EIS results indicate that the diameter of the impedance arc in the intermediate frequency region decreases with prolonged immersion. In addition, there was a significant correlation between the compressive strength and the impedance parameters (Rs and R1). Microstructural examination showed that the deterioration of the geopolymer observed was connected to depolymerization of the aluminosilicate polymers and destruction of microstructure in acidic media, which lead to loss of strength.

Jujube witches' broom (JWB) disease, associated with the presence of phytoplasmas, induces huge crop losses in the woody perennial fruit tree Ziziphus jujuba. An imbalance in the phytohormone auxin is thought to be a key factor in the development of the witches' broom symptoms, and in the alteration of floral development into leafy structures, termed phyllody. The Auxin Response Factor (ARF) gene family controls auxin-responsive gene expression during plant growth and development. However, it remains unknown if the ARF genes are involved in the formation of leaf-like flowers. In the present study, sixteen jujube ARF genes were identified bioinformatically and annotated based on the Z. jujuba cv. Dongzao genome. The ZjARFs were homologous to 12 out of the 23 Arabidopsis ARFs and were distributed in 8 jujube chromosomes and 3 unmapped scaffolds. Phylogenetic analysis grouped the ZjARFs into three classes. Spatio-temporal expression analysis revealed that the ZjARF genes were differentially expressed among different tissues during normal development. The expression of seven ZjARF genes was significantly decreased from flower buds to flowering. JWB-infected jujube plants developed the typical phyllody symptoms and showed lower auxin accumulation during floral development. ZjARF1, ZjARF2, ZjARF3, ZjARF4 and ZjARF8 resulted differentially regulated after phytoplasma infection. ZjARF4 was down-regulated before and during floral development in phytoplasma-infected plants, but it was significantly up-regulated before flowering and down-regulated during flowering in the healthy plants. Target site analysis showed that miRNA167, miRNA529 and miRNA2950 could directly target ZjARF4. Together, the data showed that the auxin-controlled ARF4 gene is likely involved in the disruption of floral development in phytoplasma-infected jujube plants.