Genome-wide identification and evolutionary analysis of MLO gene family in Rosaceae plants

Mutants lacking wild-type MLO(Mildew resistance Locus O)proteins show broad-spectrum resistance to the powdery mildew fungus,and dysregulated cell death control,with spontaneous cell death in response to developmental or abiotic stimuli.In order to understand the evolution and divergence patterns of the MLO gene family in Rosaceae plants,we analysed systematically genome-wide data from Fragaria vesca,Prunus persica,Prunus mume,Malus domestica,Pyrus bretschneideri and Rubus occidentalis based on bioinformatics methods.Using three phylogenetic methods(the neighbour-joining,maximum likelihood,and Bayesian methods),we identified 117 MLO genes from 6 Rosaceae species.The results of all three phylogenetic analysis methods supported that these genes were divided into six clades.Conserved motif analysis found that only motif 2 was present in all MLO proteins and had 3 nearly invariant amino acid residues.The findings indicated that motif 2 might be shared by the MLO gene family.The structural features of these genes showed large variations in sequence length among different species,although the lengths and the numbers of exons exhibited high degrees of similarity.Selective pressure analysis showed extremely significant differences in all 6 clades,with 2,1,and 1 site(s)under significant positive selection detected in clades III,IV,and VI,respectively.These positive selection sites were important driving forces for the promotion of the functional differentiation of the MLO genes.Functional divergence analysis showed that the significantly divergent sites were located within the domains of the MLO genes.Functional distance analysis showed that the clade V had more conservative functions and might have retained more original functions during the evolutionary process.However,clade I may have undergone extensive altered functional constraints as a specialised functional role.Moreover,the most original function of the MLO genes in Rosaceae could be related to the evolution of their resistance to powdery mildew,which then gradually evolved into functions such as the regulation of flower development,the control of root morphology,and seed evolution due to the different evolutionary rates after gene duplication.These results provide a theoretical basis for further studies of the molecular evolutionary patterns of the plant MLO gene family.

Identification of reference genes provides functional insights into meiotic recombination suppressors in Gerbera hybrida

Gerbera Hybrida is one of the important cut flowers across the world.The novel traits are the primarily market requirements and the breeding targets,mainly determined by the degree of genetic variation after hybridization.However,meiotic recombination is highly conserved in most eukaryotes which suppressed the crossover formation and limited the genetic diversity.Recently,several meiotic recombination suppressors have been identified and characterized in plants,whereas it remains elusive in G.hybrida.In order to characterize the expression patterns of these suppressors in G.hybrida,20 candidate reference genes were identified from the transcriptome datasets of G.hybrida,and their expression stabilities during plant development were evaluated by geNorm,NormFinder and BestKeeper.Although the most stable reference genes were variable in different softwares,comprehensive ranking revealed that PGK2 was the most stable reference gene and GAPDH was the most unstable one.The expression patterns of FANCM,FIGL1,RECQ4,RM1,and FLIP further validated that PGK2 was suitable for normalization of gene expression.Our study identified a reliable reference gene for gene expression during meiotic recombination,and provided functional insights into meiotic recombination suppressors in G.hybrida.

Differences in leaf physiological and morphological traits between Camellia japonica and Camellia reticulata

Plants of the genus Camellia are widely cultivated throughout the world as ornamentals because of their bright and large flowers.The widely cultivated varieties are mainly derived from the mutant lines and hybrid progenies of Camellia japonica Linn.and Camellia reticulata Lindl.While their geographical distributions and environmental adaptabilities are significantly different,no systematic comparison has been conducted between these two species.To investigate differences in how these plants have adapted to their environments,we measured photosynthesis and 20 leaf functional traits of C.japonica and C.reticulata grown under the same conditions.Compared with C.japonica,C.reticulata showed higher values for light saturation point,light-saturated photo synthetic rate,leaf dry mass per unit area and stomatal area,but lower values for apparent quantum efficiency,leaf size,stomatal density and leaf nitrogen content per unit mass.Stomatal area was positively correlated with light-saturated photosynthetic rate and light saturation point,but negatively correlated with stomatal density.The differences between C.reticulata and C.japonica were mainly reflected in their adaptations to light intensity and leaf morphological traits.C.reticulata is better adapted to high light intensity than C.japonica.This difference is related to the two species’ differing life fo rms.Thus,leaf morphological traits have played an important role in the light adaptation of C.reticulata and C.japonica,and might be first noticed and selected during the breeding process.These findings will contribute to the cultivation of camellia plants.

Identification and Expression of TOP3αin Gerbera hybrida

Meiotic recombination and the resulting novel allele combinations are fundamental to plant breeding and the identification of superior hybrids.However,the rate of meiotic crossovers is naturally suppressed below its potential ability,which prevents plant breeding efficiency.Nine suppressors of meiotic recombination have been identified in the model plant Arabidopsis and in other crop species.Mutations in these genes can lead to increased recombination frequency and could therefore potentially be used to create hyper-recombinant lines for ornamental breeding.In Gerbera hybrida,the anti-crossover factors remain elusive.In this study,we isolated and cloned TOP3αfrom flower buds of G.hybrida,and it encoded 935 amino acids with three conserved domains TOPRIM,TOP1Ac and zf-GR.Moreover,TOP3αwas the highest expressed at the flower bud stage,which coincided with the occurrence of meiotic recombination,suggesting that TOP3αis associated with the regulation of meiotic recombination in G.hybrida.

Comparative transcriptome and proteome analysis of lily clones inoculated with Fusarium oxysporum f. sp. lilii

Basal bulb rot is the major factor restricting the production of lily,caused by Fusarium oxysporum f.sp.lilii.To systematically analyze the transcriptomic and proteomic responses of lily clones to F.oxysporum,we constructed six RNA-seq libraries and four iTRAQ proteomic libraries using lily resistant and susceptible clones sampled at 0,24 and 48 h post-inoculation(hpi)with F.oxysporum respectively.137,715 unigenes were generated,of which 7,667 were differentially expressed.1,679 and 4,051 differentially expressed genes(DEGs)between resistant and susceptible clones were isolated from samples collected at 0 and 48 hpi.Four hundred and thirty three and 155 DEGs were identified in resistant clones sampled at 24 and 48 hpi separately while 550 and 799 DEGs were isolated in the susceptible clones sampled at 24 and 48 hpi respectively.The results of iTRAQ analysis revealed 7,482 proteins in resistant and susceptible clones.Data analysis of transcriptome and proteome indicated that 5,735 proteins corresponded to mRNAs.Three hundred and sixteen and 1,052 DEGs had corresponding DEPs.At 48 hpi,the resistant clones showed 155 DEGs and 108 corresponding DEPs,while the susceptible clones showed 799 DEGs and 316 corresponding DEPs.In general,these results enhance comprehension of the defense response of lily resistant clones to F.oxysporum infection and provide valuable sequence data for studying the resistance mechanism.

Morphological studies of rose prickles provide new in sights

Prickles are common structures in plants that play a key role in defense against herbivores.In the Rosa genus,prickles are widely present with great diversity in terms of form and density.For cut rose production,prickles represent an important issue,as they can damage the flower and injure workers.Our objectives were to precisely describe the types of prickles that exist in roses,their tissues of origin and their development.We performed a detailed histological analysis of prickle initiation and development in a rose F1 population.Based on the prickle investigation of 110 roses,we proposed the fi rst categorization of prickles in the Rosa genus.They are mainly divided into two categories,nonglandular prickles(NGPs)and glandular prickles(GPs),and subcategories were defined based on the presence/absence of hairs and branches.We demonstrated that NGPs and GPs both originate from multiple cells ofthe ground meristem beneath the protoderm.For GPs,the gland cells originate from the protoderm of the GP at the early developmental stage.Our findings clearly demonstrate that prickles are notmodified trichomes(which originate from the protoderm).These conclusions are different from the current mainstream hypothesis.These results provide a foundation for further studies on prickle initiation and development in plants.

Current Fertilization Practice and Phosphorus Loading from Soils near Alpine Lakes of Yunnan Province, China

Phosphorus loss from fertilization is a significant source of pollution to freshwater lakes worldwide. Production of flowers, vegetables, staple food and vineyard in regions surrounding Dianchi, Erhai, Fuxian and Xingyun lakes in Yunnan Province is large-scale. Previous studies have shown that annual fertilizer application rates (AFARs) were excessive in these regions. Significant amount of arable land near lakes has been used to build recreational parks with plants that receive less fertilization to reduce P loading. To answer whether rAFARs were associated with specific crops, AFARs of specific land uses were investigated through interviews. To estimate P loading, NaHCO3-P and NaOH-P concentrations were measured in 753 soil samples of selected layers (0 - 5, 5 - 20, 20 - 40 cm) in regions surrounding these lakes. Soil texture, pH, and cation exchange capacity (CEC) were analyzed to characterize soils. P loading was high ranging from 999 to 2094 mg P/kg as measured by NaOH-P, and levels of NaHCO3-P from 18.6 to 92.2 mg P/kg. AFARs to flower (4745 kg/ha), and vegetable (2967 kg/ha) were higher than those applied to staple food (945 kg/ha), and plants in recreation parks (200 kg/ha). The highest NaHCO3-P and NaOH-P concentrations in selected layers were associated with production of flowers, vegetables, and grapes. Although all layers of soils that were used for recreation parks in regions near Dianchi lake contained lower NaHCO3-P, NaOH-P was almost as high as with soils cultivated with flowers probably reflecting historical additions or differences in soil type. Here we show for the first time in local regions that the production of flowers, grapes and vegetables was a critical source contributing to the buildup of both readily available (NaHCO3-P) and reversibly available P (NaOH-P). Build-up of recreational parks with plants that receive less fertilization would be a long-term remediation to reduce P loading of soils in regions near Dianchi lake.

AGAMOUS correlates with the semi-double flower trait in carnation

Flower type is the most valuable ornamental trait in floricultural plants,for which the ABCDE model was proposed to explain the identity of each floral organ in flowering plants.The C-class gene AGAMOUS(AG)is responsible for stamen formation and plays an essential role in the double flower phenotype.A previous study in carnation revealed that the mutation in the miR172 binding site of the A-class gene APETALA2(AP2)leads to petal accumulation.And the expression level of AG was reduced significantly in the double flowers compared with that in the single flowers.However,there was no sequence polymorphism detected between AGs isolated from the double flowers and single flowers.Here,we performed AG analysis using single and semi-double flower carnations,and detected several mutations located in the crucial position like the MADS-box domain in the AGs of semi-double flower carnations while no changes were found at the miR172 binding site of AP2.As a result,the expression levels of AGs are reduced in the semi-double flower carnation,which could be caught by the loss function of AGs.Our data proves that AGs mutations are also associated with the semi-double flower formation in carnation,complementing the lack of research about AG-mutationassociated double flower formation in carnation.