Characteristics of long-distance mobile mRNAs from shoot to root in grafted plant species

Thousands of long-distance mobile mRNAs were identified from different grafting systems,based on high-throughput sequencing technology.Moreover,the long-distance delivery of RNAs was proved to involve multiple mechanisms.Here,we analyzed the homology,motif,and tRNA-like structure(TLS)of long-distance mobile mRNAs identified by RNA-seq as well as the RNA-binding protein(RBP)in nine grafting combinations including Arabidopsis thaliana,Vitis vinifera,Cucumis sativus,Citrullus lanatus,Nicotiana benthamiana,Malus domestica,Pyrus spp.,Glycine max and Phaseolus vulgaris.Although several mRNAs were found to be shared in herbaceous,woody,and related species,the vast majority of long-distance mobile mRNAs were species-specific.Four non-specific movement-related motifs were identified,while the TLS was not necessary for mRNA long distance mobility.In addition,we found that RBPs were conserved among herbaceous and woody plants as well as related species.This paper reports a further in-depth analysis of the endogenous mechanisms by which the species-specific transportable m RNAs were selected by bioinformatics,in order to provide insights for future research on long-distance mobile mRNAs.

Genome-wide identification and characterization of the IPT family members in nine Rosaceae species and a functional analysis of MdIPT5b in cold resistance

Cytokinins are members of a group of phytohormones involved in various growth and developmental processes in plants.Isopentenyl transferase(IPT)is the rate-limiting enzyme in catalyzing the biosynthesis of cytokinins.In this study,to understand the role of IPT family in cold resistance,78 IPT candidates were identified and characterized in nine Rosaceae genomes.The expansion of IPT families in the Rosaceae primarily occurred through segmental duplication rather than tandem duplication.In general,purifying selection controlled the evolution of IPT families in the Rosaceae,with IPT3 and IPT5 homologs as the primary drivers of evolution.Cis-elements,which are involved in the responses to many environmental stresses or phytohormone signals,were identified in the promoters of MdIPT members.This was consistent with the trends of expression of the MdIPT genes in apple(Malus domestica)calli.MdIPT5b was also found to exhibit multiple responses to phytohormones and stress signals.The ectopic expression of MdIPT5b resulted in an increase in cold resistance in transformed apple calli and tomato(Solanum lycopersicum)plantlets.The redox balance was partially stabilized through the accumulation of proline under cold stress.However,the ascorbate–glutathione cycle cannot be stabilized in the cold.All physiological and biochemical assays are preformed in spectrophotometer.These results showed that regulating the expression of IPT genes for moderate cytokinin improvement could enhance the accumulation of proline to stabilize the osmotic and redox balances to improve resistance to cold stress.

Niche differentiation shapes the bacterial diversity and composition of apple

Microorganisms play an important role in plant growth,health and ecological function.It is necessary to explore the microbial community because of the significant ecological and economic value of apples(Malus x domestica).However,the related bacterial communities in different ecological habitats are not clear in the unique scion/rootstock combinations of apples.In this study,the Illumina Miseq platform was used to analyze the bacterial communities in different niches(bulk soil,rhizosphere soil and roots)of two scion/rootstock combinations[Fuji/Malus xiaojinensis Cheng et Jiang(Mx)and Fuji/Malus baccata(L.)Borkh.(Mb)].The relationship between the microbial community,soil properties,and plant characters was explored.The results showed that the diversity of the bacterial community decreased from bulk soil to rhizosphere soil and then to roots.In addition,at the phylum level,Proteobacteria,Actinobacteria and Acitinobacteria were dominant and had notable divergence in different ecological niches.Distinct niches had remarkable effects on the diversity and composition of the bacterial community according to PCoA.The rootstock genotype had an effect on the bacterial composition but no effect on the diversity.pH,soil organic matter(SOM),alkaline hydrolyzable nitrogen(AN)were the main factor affecting the structure of bacterial community in rhizosphere soil,as shown by Pearson analysis.Bacteria taxa in the roots were affected by starch,fructose,sucrose and sorbitol.This study showed the microbial community structure in different ecological niches of different scion/rootstock combinations and provided some evidence for understanding the microbial-plant interaction of apple rootstocks.

Molecular and physiological characterization of the effects of auxin-enriched rootstock on grafting

Grafting is a highly useful technique,and its success largely depends on graft union formation.In this study,we found that root-specific expression of the auxin biosynthetic gene iaaM in tobacco,when used as rootstock,resulted in more rapid callus formation and faster graft healing.However,overexpression of the auxin-inactivating iaaL gene in rootstocks delayed graft healing.We observed increased endogenous auxin levels and auxin-responsive DR5::GUS expression in scions of WT/iaaM grafts compared with those found in WT/WT grafts,which suggested that auxin is transported upward from rootstock to scion tissues.A transcriptome analysis showed that auxin enhanced graft union formation through increases in the expression of genes involved in graft healing in both rootstock and scion tissues.We also observed that the ethylene biosynthetic gene ACS1 and the ethylene-responsive gene ERF5 were upregulated in both scions and rootstocks of the WT/iaaM grafts.Furthermore,exogenous applications of the ethylene precursor ACC to the junction of WT/WT grafts promoted graft union formation,whereas application of the ethylene biosynthesis inhibitor AVG delayed graft healing in WT/WT grafts,and the observed delay was less pronounced in the WT/iaaM grafts.These results demonstrated that elevated auxin levels in the iaaM rootstock in combination with the increased auxin levels in scions caused by upward transport/diffusion enhanced graft union formation and that ethylene was partially responsible for the effects of auxin on grafting.Our findings showed that grafting success can be enhanced by increasing the auxin levels in rootstocks using transgenic or gene-editing techniques.

ERF4 affects fruit ripening by acting as a JAZ interactor between ethylene and jasmonic acid hormone signaling pathways

The regulation of apple(Malus domestica)fruit texture during ripening is complex and a fundamental determinant of its commercial quality.In climacteric fruit,ripening-related processes are regulated by ethylene(ET),and jasmonate(JA)is also involved in the ethylene biosynthesis pathway,mainly through the transcription factor MYC2.However,the molecular genetic mechanism for fruit ripening processes between the JA and ET signaling pathways still needs to be elucidated.In order to explore how JA regulates apple fruit ripening through ERF4,we used’Gala’and’Ralls Janet’fruit at different developmental stages as experimental materials to determine the fruit firmness and related gene expression analysis.Meanwhile,we carried out different hormone treatments on’Gala’fruit at ripening stage.Here,we show that ERF4 is a core JA signaling hub protein JASMONATE ZIM-DOMAIN(JAZ)interactor that affects ethylene signaling pathways.During fruit development,ERF4 represses the expression of ACS1 and ACO1 by interacting with JAZ,as well as with the JA-activated transcription factor MYC2.Ripening is promoted in JAZ-suppressed apples.Thus,ERF4 acts as a molecular link between ethylene and JA hormone signals,and the natural variation of the ERF4Ethylene-responsive binding factor-associated amphiphilic repression(EAR)motif decreases repression of ethylene biosynthesis genes.

Progress of Apple Rootstock Breeding and Its Use

Apple rootstock breeding has achieved great progress worldwide.In this review,we first summarize the rootstock breeding targets and utilization in main apple-producing countries.Furthermore,we discuss the focus and important research areas of apple rootstock breeding through five aspects:parent selection and setting of crosses,target genes and marker-assisted breeding,root configuration-guided breeding,apomictic resource utilization,and the application of genetic engineering.Finally,we propose an apple rootstock division plan for China,which has a large potential to provide guidance for apple rootstock breeding and utilization in different apple-producing areas of China.