Polyamine (PA) catabolic processes are performed by copper-containing amine oxidases (CuAOs) and flavin-containing PA oxidases (PAOs). So far, several CuAOs and PAOs have been identified in many plant species. These enzymes exhibit different subcellular localization, substrate specificity, and functional diversity. Since PAs are involved in numerous physiological processes, considerable efforts have been made to explore the functions of plant CuAOs and PAOs during the recent decades. The stress signal transduction pathways usually lead to increase of the intracellular PA levels, which are apoplastically secreted and oxidized by CuAOs and PAOs, with parallel production of hydrogen peroxide (H2O2). Depending on the levels of the generated H2O2, high or low, respectively, either programmed cell death (PCD) occurs or H2O2 is efficiently scavenged by enzymatic/nonenzymatic antioxidant factors that help plants coping with abiotic stress, recruiting different defense mechanisms, as compared to biotic stress. Amine and PA oxidases act further as PA back-converters in peroxisomes, also generating H2O2, possibly by activating Ca2+ permeable channels. Here, the new research data are discussed on the interconnection of PA catabolism with the derived H2O2, together with their signaling roles in developmental processes, such as fruit ripening, senescence, and biotic/abiotic stress reactions, in an effort to elucidate the mechanisms involved in crop adaptation/survival to adverse environmental conditions and to pathogenic infections.

Summary: Co‐infection of apple trees with several viruses/viroids is common and decreases fruit yield and quality. Accurate and rapid detection of these viral pathogens helps to reduce losses and prevent virus spread. Current molecular detection assays used for apple viruses require specialized and expensive equipment. Here, we optimized a CRISPR/Cas12a‐based nucleic acid detection platform for the diagnosis of the most prevalent RNA viruses/viroid in apple, namely Apple necrotic mosaic virus (ApNMV), Apple stem pitting virus (ASPV), Apple stem grooving virus (ASGV), Apple chlorotic leaf spot virus (ACLSV) and Apple scar skin viroid (ASSVd). We detected each RNA virus/viroid directly from crude leaf extracts after simultaneous multiplex reverse transcription‐recombinase polymerase amplification (RT‐RPA) with high specificity. Positive results can be distinguished by the naked eye via oligonucleotide‐conjugated gold nanoparticles. The CRISPR/Cas12a‐RT‐RPA platform exhibited comparable sensitivity to RT‐qPCR, with limits of detection reaching 250 viral copies per reaction for ASPV and ASGV and 2500 copies for the others. However, this protocol was faster and simpler, requiring an hour or less from leaf harvest. Field tests showed 100% agreement with RT‐PCR detection for 52 samples. This novel Cas12a‐based method is ideal for rapid and reliable detection of apple viruses in the orchard without the need to send samples to a specialized laboratory.

Summary: Plant stature is one important factor that affects the productivity of peach orchards. However, little is known about the molecular mechanism(s) underlying the dwarf phenotype of peach tree. Here, we report a dwarfing mechanism in the peach cv. FenHuaShouXingTao (FHSXT). The dwarf phenotype of ‘FHSXT’ was caused by shorter cell length compared to the standard cv. QiuMiHong (QMH). ‘FHSXT’ contained higher endogenous GA levels than did ‘QMH’ and did not response to exogenous GA treatment (internode elongation). These results indicated that ‘FHSXT’ is a GA‐insensitive dwarf mutant. A dwarf phenotype‐related single nucleotide mutation in the gibberellic acid receptor GID1 was identified in ‘FHSXT’ (GID1c^S191F), which was also cosegregated with dwarf phenotype in 30 tested cultivars. GID1c^S191F was unable to interact with the growth‐repressor DELLA1 even in the presence of GA. ‘FHSXT’ accumulated a higher level of DELLA1, the degradation of which is normally induced by its interaction with GID1. The DELLA1 protein level was almost undetectable in ‘QMH’, but not reduced in ‘FHSXT’ after GA₃ treatment. Our results suggested that a nonsynonymous single nucleotide mutation in GID1c disrupts its interaction with DELLA1 resulting in a GA‐insensitive dwarf phenotype in peach.

Jujube witches’ broom (JWB) is caused by infection with a phytoplasma. A multi-omics approach was taken during graft infection of jujube by JWB-infected scion through the analysis of the plant transcriptome, proteome and phytohormone levels. A high number of differentially expressed genes (DEGs) were identified 37 weeks after grafting (WAG), followed by observation of typical symptoms of JWB at 48 WAG. At 37 WAG, the majority of the upregulated DEGs and differentially expressed proteins (DEPs) were related to flavonoid biosynthesis, phenylalanine metabolism and phenylpropanoid biosynthesis. Two of the four upregulated proteins were similar to jasmonate-induced protein-like. Among the downregulated genes, the two most populated GO terms were plant–pathogen interaction and plant hormone signal transduction (mainly for tryptophan metabolism). Moreover, phytoplasma infection resulted in reduced auxin content and increased jasmonate content, indicating that auxin and jasmonic acid have important roles in regulating jujube responses during the first and second stages of phytoplasma infection. At 48 WAG, the two largest groups of upregulated genes were involved in phenylpropanoid biosynthesis and flavonoid biosynthesis. Both genes and proteins involved in carbon metabolism and carbon fixation in photosynthetic organisms were downregulated, indicating that photosynthesis was affected by the third stage of phytoplasma infection.

Peach (Prunus persica L. Batsch) trees grow vigorously and are subject to intense pruning during orchard cultivation. Reducing the levels of endogenous gibberellins (GAs) represents an effective method for controlling branch growth. Gibberellin 2-oxidases (GA2oxs) deactivate bioactive GAs, but little is known about the GA2ox gene family in peach. In this study, we identified seven PpGA2ox genes in the peach genome, which were clustered into three subgroups: C₁₉-GA2ox-I, C₁₉-GA2ox-II, and C₂₀-GA2ox-I. Overexpressing representative genes from the three subgroups, PpGA2ox-1, PpGA2ox-5, and PpGA2ox-2, in tobacco resulted in dwarf plants with shorter stems and smaller leaves than the wild type. An analysis of the GA metabolic profiles of the transgenic plants showed that PpGA2ox-5 (a member of subgroup C₁₉-GA2ox-II) is simultaneously active against both C₁₉-GAs and C₂₀-GAs,which implied that C₁₉-GA2ox-II enzymes represent intermediates of C₁₉-GA2oxs and C₂₀-GA2oxs. Exogenous GA₃ treatment of shoot tips activated the expression of all seven PpGA2ox genes, with different response times: the C₁₉-GA2ox genes were transcriptionally activated more rapidly than the C₂₀-GA2ox genes. GA metabolic profile analysis suggested that C₂₀-GA2ox depletes GA levels more broadly than C₁₉-GA2ox. These results suggest that the PpGA2ox gene family is responsible for fine-tuning endogenous GA levels in peach. Our findings provide a theoretical basis for appropriately controlling the vigorous growth of peach trees.

Summary: Peach (Prunus persica) is one of the most important fruit crops globally, but its cultivation can be hindered by large tree size. ‘Zhongyoutao 14’ (CN14) is a temperature‐sensitive semi‐dwarf (TSSD) cultivar which might be useful as breeding stock. The genome of CN14 was sequenced and assembled de novo using single‐molecule real‐time sequencing and chromosome conformation capture assembly. A high‐quality genome was assembled and annotated, with 228.82 Mb mapped to eight chromosomes. Eighty‐six re‐sequenced F₁ individuals and 334 previously re‐sequenced accessions were used to identify candidate genes controlling TSSD and flower type and size. An aquaporin tonoplast intrinsic protein (PpTIP2) was a strong candidate gene for control of TSSD. Sequence variations in the upstream regulatory region of PpTIP2 correlated with different transcriptional activity at different temperatures. PpB3‐1, a candidate gene for flower type (SH) and flower size, contributed to petal development and promoted petal enlargement. The locus of another 12 agronomic traits was identified through genome‐wide association study. Most of these loci exhibited consistent and precise association signals, except for flesh texture and flesh adhesion. A 6015‐bp insertion in exon 3 and a 26‐bp insertion upstream of PpMYB25 were associated with fruit hairless. Along with a 70.5‐Kb gap at the F‐M locus in CN14, another two new alleles were identified in peach accessions. Our findings will not only promote genomic research and agronomic breeding in peach but also provide a foundation for the peach pan‐genome.