Analysis of the Germplasm Resources and Genetic Relationships Among Hybrid Cymbidium Cultivars and Native Species with RAPD Markers

The random amplified polymorphic DNA （RAPD） marker was assessed to detect the genetic relationships among 48 hybrid Cymbidium cultivars from Japan, Korea, China, and USA, and 2 species of native Cymbidium. Twenty primers were screened from 100 random decamer primers, and a total of 258 DNA bands were amplified, 253 of which （98.1%） were polymorphic. The average number of polymorphic DNA bands amplified by each primer was 12.6. All cultivars were distinguishable when a number of primers were considered. Genetic similarities among the cultivars and species were estimated based on the amount of band sharing ranging from 0.364-0.817 with an average of 0.581. According to the data, a dendrogram of genetic relationship, which was constructed using the UPGMA method, showed that all the tested cultivars and native species were classified into five cluster groups with the similarity coefficient of 0.592. It revealed that the genetic relationships among tested accessions were to some extent related with their origin, flower colour, branch type, and genealogy. It further indicated that the RAPD technique is a useful tool for studying the genetic relationships among hybrid Cymbidium cultivars.

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.

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.

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.

An auxin‐responsive endogenous peptide regulates root development in Arabidopsis

Auxin plays critical roles in root formation and development. The components involved in this process, however, are not well understood. Here, we newly identified a peptide encoding gene, auxin-responsive endogenous polypeptide 1 （AREP1）, which is induced by auxin, and mediates root development in Arabidopsis. Expression of AREP1 was specific to the cotyledon and to root and shoot meristem tissues. Amounts of AREP1 transcripts and AREP1-green fluorescent protein fusion proteins were elevated in response to indoleacetic acid treatment. Suppression of AREP1 through RNAi silencing resulted in reduction of primary root length, increase of lateral root number, and expansion of adventitious roots, compared to the observations in wild-type plants in the presence of auxin. By contrast, transgenic plants overexpressing AREP1 showed enhanced growth of the primary root under auxin treatment. Additionally, rootmorphology, including lateral root number and adventitious roots, differed greatly between transgenic and wildtype plants. Further analysis indicated that the expression of auxin-responsive genes, such as IAA3, IAA7, IAA17, GH3.2, GH3.3, and SAUR-AC1, was significantly higher in AREP1 RNAi plants, and was slightly lower in AREP1 overexpressing plants than in wildtype plants. These results suggest that the novel endogenous peptide AREP1 plays an important role in the process of auxinmediated root development.