The jujube (Ziziphus jujuba Mill.), a member of family Rhamnaceae, is a major dry fruit and a traditional herbal medicine for more than one billion people. Here we present a high-quality sequence for the complex jujube genome, the first genome sequence of Rhamnaceae, using an integrated strategy. The final assembly spans 437.65 Mb (98.6% of the estimated) with 321.45 Mb anchored to the 12 pseudo-chromosomes and contains 32,808 genes. The jujube genome has undergone frequent inter-chromosome fusions and segmental duplications, but no recent whole-genome duplication. Further analyses of the jujube-specific genes and transcriptome data from 15 tissues reveal the molecular mechanisms underlying some specific properties of the jujube. Its high vitamin C content can be attributed to a unique high level expression of genes involved in both biosynthesis and regeneration. Our study provides insights into jujube-specific biology and valuable genomic resources for the improvement of Rhamnaceae plants and other fruit trees.

Plant pathogens secrete proteins, known as effectors, that function in the apoplast and inside plant cells to promote virulence. Effectors can also be detected by cell-surface and cytosolic receptors, resulting in the activation of defence pathways and plant immunity. Our understanding of fungal effector function and detection by immunity receptors is limited largely due to high sequence diversity and lack of identifiable sequence motifs precluding prediction of structure or function. Recent studies have demonstrated that fungal effectors can be grouped into structural classes despite significant sequence variation. Using protein x-ray crystallography, we identify a new structural class of effectors hidden within the secreted in xylem (SIX) effectors from Fusarium oxysporum f. sp. lycopersici (Fol). The recognised effectors Avr1 (SIX4) and Avr3 (SIX1) represent the founding members of the Fol dual-domain (FOLD) effector class. Using AlphaFold ab initio protein structure prediction, benchmarked against the experimentally determined structures, we demonstrate SIX6 and SIX13 are FOLD effectors. We show that the conserved N-domain of Avr1 and Avr3 is sufficient for recognition by their corresponding, but structurally-distinct, immunity receptors. Additional structural prediction and comparison indicate that 11 of the 14 SIX effectors group into four structural families. This revealed that genetically linked effectors are related structurally, and we provide direct evidence for a physical association between one divergently-transcribed effector pair. Collectively, these data indicate that Fol secretes groups of structurally-related molecules during plant infection, an observation that has broad implications for our understanding of pathogen virulence and the engineering of plant immunity receptors.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. AbstractLeaf rust, caused by Puccinia triticina, is one of the most destructive fungal diseases in wheat production worldwide. The hypersensitive reaction (HR) is an important defence response against P. triticina infection. In this study, the physiological races 165 and 260 of P. triticina were combined with a line derived from the bread wheat cultivar Thatcher with the leaf rust resistance locus Lr26 to form compatible and incompatible combinations, respectively. Based on an RNA-Seq database of the interaction systems, a new wheat cysteine-rich receptor-like kinase gene, TaCRK2, is specifically induced and up-regulated in the incompatible combination. We identified that TaCRK2 was regulated in a Ca 2+ -dependent manner. Knockdown of TaCRK2 by virus-induced gene silencing and RNAi leads to a dramatic increase in HR area and the number of haustorial mother cells at the single infection site. In addition, urediniospores, a P. triticina-specific pathogenic marker in compatible combinations, were observed on leaf surfaces of silenced plants at approximately 15 days after inoculation in the incompatible combination. Moreover, transcription levels of TaPR1, TaPR2, and TaPR5 were obviously reduced in TaCRK2-silenced plants. TaCRK2 overexpression in Nicotiana benthamiana induced strong HR-like cell death. Finally, transient expression of green fluorescent protein fused with TaCRK2 in N. benthamiana indicated that TaCRK2 localizes in the endoplasmic reticulum. Thus, TaCRK2 plays an important role in the resistance to P. triticina infection and has a positive regulation effect on the HR cell death process induced by P. triticina. K E Y W O R D S cysteine-rich receptor-like protein kinase, hypersensitive reaction, Puccinia triticina, VIGS, wheat | 733 GU et al.

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