This review briefly describes the carotenoid metabolic pathway and main flux-controlling steps for carotenoid accumulation in plants. It highlights our recent understanding of the regulatory mechanisms underlying carotenoid accumulation at transcriptional，post-transcriptional，post-translational and epigenetic levels.

Citrus is usually considered as a typical non-climacteric fruit，with abscisic acid being primarily associated with citrus fruit maturity. However，other hormones，such as ethylene，gibberellin，auxin，also contribute significantly to the maturity and color transition of citrus. In production，a variety of natural hormones and synthetic plant growth regulators are commonly utilized to extend the marketing period of citrus fruits and improve postharvest preservation. This paper provides a comprehensive review of current research advances concerning the role of plant hormones on the maturation of citrus fruits. It delves into the complex relationships between these hormones and investigates the regulatory mechanisms controlled by related transcription factors. The primary aim is to provide reference for further research.

The methods for QTL identification of important traits in fruit trees by genetic linkage map，BSA and GWAS are expounded and compared. The current review summarizes advancement on the identification of QTLs associated with important traits of fruit trees，including external appearance，internal quality，growth and development，resistance to biotic and abiotic stress，in recent years. The purpose of this review is to provide clues for understanding the QTL identification and breeding of fruit tree，and to discuss and propose the methods and strategies that can be used for QTL identification and mapping of important characters in fruit trees.

In this review，recent studies on the relationship between fruit sugar accumulation and sugar transporters （mainly includes sucrose transporter SUT related to sucrose accumulation，hexose transporter STP related to hexose accumulation，tonoplast sugar transporter TST that is highly related to vacuolar sugar accumulation，early response to dehydration six like protein ERDL6 related to vacuolar glucose efflux，sugar transporter SWEET newly identified in plants in recent years，and sorbitol transporter SOT，which is unique to Rosaceae plants，etc）in horticultural crops were summarized，and discussed prospects for future research directions on sugar transporters and the molecular biology method for fruit quality improvement.

Sugar is an important factor that determines fruit quality of citrus. Illustrating the characteristic and regulation mechanism of citrus fruit sugar metabolism and transport will greatly contribute to regulating sugar accumulation accurately. In this paper，the mechanisms underlying sugar accumulation were comprehensively reviewed，we also summarized the differences of fruit sugar accumulation in various citrus varieties，the characteristics of sugar accumulation with fruit development and the relationship between sugar and the related enzyme activities. Subsequently，a model of metabolic differences between sucrose accumulation type and hexose accumulation type was mapped in citrus. Moreover，the storage process of sucrose from leaf（source organ）to fruit（sink organ）was described systematically，including phloem loading，unloading，transport and sucrose storage in fruit vacuole. Finally，a model of sugar transport from source to sink was constructed in citrus.

This paper reviews the achievements of Cymbidium germplasm resources，breeding and the molecular research of main ornamental traits. Germplasm resources are the basis for the breeding of Cymbidium. China is the distribution center of this genus with 57 species out of 83 species in the world，and have been formed a large number of traditional varieties which domesticated since 2 500 years ago. To date，the breeding method is still focused on traditional hybridization. There are more than 17 000 Cymbidium hybrids registered on RHS，and 43 new Cymbidium cultivars authorized by the Ministry of Agriculture and Rural Affairs of China. More importantly，Genetic engineering breeding will be the key direction of Cymbidium breeding in the future. A batch of structural genes and transcription factors involved in the main ornamental traits have been unearthed through transcriptome and genome and some of them have been functionally verified，which layed the foundation for the transformation of Cymbidium from traditional breeding to molecular breeding.

Crispy loss is an important reason for reducing the fruit quality of horticultural crops and consumers’ desire to purchase. As a comprehensive concept that includes sound conduction，geometric characteristics and fracture characteristics，the fruit crispy is affected by the cell state，the mechanical strength of the cell wall and the turgor pressure. In-depth understanding of fruit crispy，clarifying crispy evaluation methods and the physiological and biochemical changes in the process of crispy change not only provide a theoretical basis for the production of high-quality fruit，but also provide an important guidance for increasing yield and income. This article summarizes the perceptual process and evaluation of fruit crispy，the factors affecting the crispy and the important progress in related physiological and biochemical metabolism.

Perennial monocots have special underground buds，ground buds，and underground organs. Their dormancy characteristics are obviously different from those of eudicots with aboveground buds. This review article summarized the regulation mechanisms of winter dormancy from environmental，hormonal and carbohydrate in monocots. The regulation mechanisms and research progress of winter dormancy in perennial monocots and eudicots were compared. Combined with the current research progress，suggestions for future directions on the study of winter dormancy regulation in perennial monocots were provided.

Fruit chloroplast quantity and function have a direct impact on fruit quality. Fruit chloroplasts function as assimilation organs before ripening，synthesizing amounts of assimilates for fruit development and quality-related metabolites synthesis，and transform into chromoplasts during ripening，storing nutrients and flavor substances synthesized by different metabolic pathways driven by photosynthesis in the early stage. As a result，increasing fruit quality by controlling chloroplast development has been a research emphasis，and significant progress has been made in the study of fruit chloroplast developmental regulation in tomatos an essential fruit vegetable and model plant. This manuscript reviewed the progress of tomato fruit chloroplast development regulation in terms of transcription factors，light signals，hormone signals，and oxidative stress signals，as well as the challenges and future research directions，to clarify the specific regulation mechanism of fruit chloroplast development and provide new ideas for fruit quality improvement of tomato and other crops.

Orchid senescence caused by the external factors，the metabolic changes of internal organization during the senescence process，and the molecular mechanism of ethylene synthesis and signal transduction pathway regulating orchid senescence were reviewed. The common commercially popular fresh-keeping treatment technologies for cut and potted orchids and their application effects after treatment，and the improvement of orchid senescence-related genes were summarized. Additionally，modern genetic engineering technologies to delay the orchids senescence process and prolong the ornamental time by regulating functional genes were prospected.

This review focused on the recent research findings related to cucumber plant architecture involving genetic pattern，QTL mapping and gene cloning. The molecular were summarized basic research progress in seven aspects：plant height，determinate / indeterminate growth pattern，hypocotyl length，leaf shape，leaf size，lateral branch development ability，and tendril development. The existing related research gaps and shortcomings were analyzed，and a way forward for the development of the ideal plant architecture of cucumber was proposed. The key research directions highlighted in this review will provide a reference for the breeding of the ideal plant architecture of cucumber.

The Pepper originated in the semi-arid area in central and southern Bolivia where the annual rainfall is less than 500 mm. This is a subtropical frost-free area. The original wild species are perennial herbs. According to the analysis and study of the starch granules,the Capsicum starch microfossils have been found dating from 8 000-7 500 years ago. Over thousands of years,Capsicum seeds spread out from Bolivia with the help of birds and indigenous peoples,thus spreading throughout South and Central America,then to the southwest of North America. In different ecological regions,more than 10 wild relatives and about 20 wild non-relatives of cultivated species have evolved. Capsicum cultivars evolved from the common ancestor Capsicum chacoense. The purple flower ancestors migrated to the Andes highlands and evolved to Capsicum pubescens. And the white flower ancestors migrated to the relatively dry area of southern Bolivia to evolve to Capsicum baccatum,continuing to migrate to the humid Amazon basin and evolve to the common ancestors of Capsicum annuum,Capsicum frutescens L. and Capsicum chinense Jacquin. They continued to migrate outward,evolving Capsicum annuum in Mexico and northern Central America,Capsicum frutescens L. in the Caribbean,and Capsicum chinense Jacquin in the northern valleys of the Amazon Basin. The pepper domestication started by removing the wild species from the original area for artificial cultivation. The wild species with the fruit small,single-color,upward-facing and easily falling off were domesticated into cultivated species with the fruit succulent,various-shaped,colorful,downward-facing,and not easy falling off,i.e. good economic benefits. Capsicum annuum was the first cultivated species domesticated in Mexico and Central America more than 6 000 years ago,and the other four cultivated species had been cultivated for at least 4 000 years,which are the oldest cultivated plants in America.

In this study，Camellia sinensis phytoene desaturase gene（CsPDS）and tea caffeine synthase gene（TCS1）as indicator genes and Nicotiana benthamiana as a vector were employed to enrich tobacco rattle virus. The effects of the concentration of infiltration solution，incubation temperature，different vectors and incubation time on the enriched viruses were investigated，with N. benthamiana used as the vector to enrich the viruses. The effects of different inoculation methods and cultivars on the construction of a virus-induced gene silencing（VIGS）system were also investigated in tea plant. The results demonstrated that inoculation of tobacco with acetosyringone（AS）at a concentration of 200 μmol · L^-1 bacteriophage with an optical density（OD₆₀₀）of 1.0 was conducive to virus enrichment in tobacco when incubated at 23 ℃. The leaves of‘Shuchazao’were used to construct the VIGS system of tea plant by injection inoculation, and the system was successfully used to explore the possibility of foreign gene expression with GFP as the indicator gene.

Citrus genetic improvement has achieved a great progress during the last six decades in China. A repository harboring more than 1 700 accessions of Rutaceae in Chongqing and an embryogenic callus collection including more than 100 varieties in Wuhan have been established,respectively. Continuing exploration of citrus germplasm resulted in the identification of wild Daoxian tangerine,Honghe papeda and the mini-citrus,a mono-embryonic Hongkong kumquat for functional genmics research. A new type of rootstock,Ziyang Xiangcheng（Citrus junos）has been utilized in Chinese citrus industry. A total of 122 citrus varieties including 121 for scion and one for rootstock have been registered or protected by PVP. Out of the scion varieties,88.5% is from the natural mutation including the bud-sport and chance seedling variation,and the rest from artifically created mutants,such as the irradiation,hybridization and protoplast fusion etc. These varieties covered nearly all types of citrus,including loose-skin mandarin,sweet orange and pummelo etc,with improved seedlessness,mature season and fruit color etc. The omics technologies have been widely used in citrus genetic improvement in China. Genomes including sweet orange and other main citrus species have been sequenced and assembled during the recent decade,as has accelerated cloning of the key genes controlling import agronomic traits,such as the polyembryonic related gene CitRWP etc. Genetic transformation and gene editing are also setup in Citrus. These achievments have laid a solid base for citrus genome-design breeding for the future.

Proton pumps are types of important enzymes that promote proton（H⁺）transmembrane transport and cause potential difference between the membrane and participate in a variety of life processes. Organic acids are mainly stored in vacuoles and proton pump promotes proton transmembrane transport accompanied by energy release，which then provides power for the transmembrane transport and storage of organic acids in vacuoles. This paper focuses on the categories，structural characteristics and regulatory factors of proton pumps related to acid transport in horticultural plants，as well as the research status of different types of proton pumps in the regulation of organic acid accumulation，in order to provide reference for the research and regulation of proton pumps and organic acid accumulation in horticultural plants，and then provide a theoretical basis for regulating the quality of horticultural plants.

Crassulacean acid metabolism photosynthetic pathway is a kind of carbon concentrating mechanism that evolved from C3 photosynthesis and it is characterized by nocturnal CO₂ fixation and high water use efficiency. Currently，there are growing interests in improving WUE to enhance drought resistance by“transferring”CAM pathway into C₃ crops，also called‘CAM engineering’. CAM engineering has significant application potential in agriculture，while systematical investigations of CAM photosynthetic pathway / plants are a prerequisite to its progression. The wide applications of multi-omics and molecular biology methods have extensively promoted CAM plants related studies. CAM pathway-related key genes and their functions are being gradually revealed，and many CAM plant genomes have been published. Diverse mechanisms are involved in the regulation of the CAM pathway, including transcription factors，hormones，miRNA，lncRNA，alternative splicing，and DNA methylation This article mainly focuses on the latest progress of molecular biology and omics studies on CAM plants. In addtion，future research prospective and study interests are also discussed to guide further investigations on CAM plants.

In this study，high temperature experiment was conducted and phylogenetic index were analyzed using Rosa chinensis‘Angela’‘Renyue’and‘Xianjing’as test materials. The results showed that‘Angela’exhibited the highest heat resistance among the three varieties. Comparative transcriptome analysis，co-expression network analysis，protein-protein interaction network analysis and phylogenetic analysis revealed that the improvement of heat tolerance in‘Angela’is associated with the overexpression of heat shock transcription factors（HSFs）and heat shock proteins（HSPs）. Notably，the expression level of HSP gene RcHSP18.1 significantly increased with prolonged heat stress duration. Furthermore，by silencing the homologous gene NtHSP18.1 in tobacco，the heat resistance of tobacco was significantly reduced，confirming the essential role of HSP18.1 in heat stress tolerance. Overexpressing of RcHSP18.1 through gene bombardment and silencing RcHSP18.1 gene by virus induced gene silencing technique have both confirmed the significant role the gene RcHSP18.1 in enhancing heat stress resistance in‘Angela’.

Flavonoids are a class of secondary metabolites with ‘flavan’ skeleton and thousands of derivatives. The biosynthetic pathways of flavonoids are complicated，and some of them and related enzymes have been analyzed. Flavonoids play important roles in the growth and development of plants and the formation of flowers and fruits. Studies revealed that flavonoids can response to stresses and improve the tolerance and resistance of plants. This article reviews the biosynthetic pathways and molecular regulation mechanism of flavonoids in plants，the response of flavonoid pathways to different stresses，the main roles and mechanisms of flavonoids，and the future research directions. Thus，this article is expected to providing theoretical support for the targeted cultivation of horticultural crop varieties with highly resistant，deep processing，and product development.

This paper introduces the important achievements of pepper breeding over the past 60 years in China. It includes the collection,identification,evaluation,utilization and exploration of germplasm resources. The paper also discusses the important advancement in breeding technologies which includes heterosis utilization,anther culture,marker-assisted selection（MAS）,multiple resistance breeding and shuttle breeding. In addition,the history of pepper breeding is reviewed,including the traditional breeding before 1980s and the modern breeding guided with National scientific and technological research after 1980s. Then,driven by the industrial demands,China's pepper breeding has been undergoing several major optimizations：increasing yield,adjusting growth period,enhancing disease resistance,breeding for easy storage and transportation,breeding processed-food-specific varieties,improving product quality,and breeding for mechanized harvesting. After more than four decades of development,a modern and world-leading commercial pepper breeding system has been completely established. Domestic varieties with independent intellectual property rights are taking over 95% of market share across the country. Meanwhile,there are several unique advantages of in China's pepper breeding industry,such as low barrier to entry,low risk,high efficiency,large team,rich varieties,and high effectiveness. However,there are also several problems that strongly restrict the development of the pepper seed industry in China,including homogenization of pepper varieties,difficulty in expanding pepper seed business enterprises and slow research progress of pepper molecular breeding technology. Long-season varieties cultivated in green house and ornamental pepper varieties are mainly imported because the pepper breeding in China is still lagging behind developed countries. Therefore,the future directions for pepper breeding in China will be improving product quality,producing varieties suitable for mechanized production,breeding varieties with medicinal or other functional ingredients,exploring and advertising local varieties with excellent properties,and innovating novel breeding technologies.

To evaluate the effect of apple dwarfing rootstocks on the scion growth and drought resistance,we used four-year-old apple trees with different scion-rootstock combinations（‘Fuji’/G935,‘Fuji’/M9-T337 and‘Fuji’/SH6）. Morphology analysis of these three apple trees showed that‘Fuji’scion grown on SH6 exhibited significantly reduced leaf thickness,palisade tissue thickness and stomatal density compared with the‘Fuji’grafted on G935 and M9-T337. Furthermore,three kinds of apple trees were exposed to drought stress treatment for determining their drought tolerance and recovery feature after re-watering. The analysis of drought-related physiology parameters indicated that compared with the other two grafted combinations,the‘Fuji’/SH6 combination displayed enhanced water use efficiency（WUE）,osmoregulation substance content,superoxide dismutase（SOD）activity and ABA content,and the reduced malondialdehyde（MDA）content,net photosynthetic rate（P_n）,transpiration rate（T_r）and stomatal conductance（G_s）under drought stress. The results of membership function analysis showed that‘Fuji’/SH6 had the optimal drought resistance,followed by‘Fuji’/G935,and‘Fuji’/M9-T337 had the worst drought resistance. Overall,‘Fuji’/SH6 grafted combination showed excellent drought resistance.