A chromosome-level genome assembly for Chinese plum‘Wushancuili'reveals the molecular basis of its fruit color and susceptibility to rain-cracking

Chinese plum(Prunus salicina Lindl.)originates from China and makes a large contribution to the global production of plums.The P.salicina‘Wushancuili'has a green coloration and high fruit quality and is economically important in eliminating poverty and protecting ecology in the Yangtze River Three Gorges Reservoir.However,rain-induced cracking(rain-cracking,literally skin cracking caused by rain)is a limitation to‘Wushancuili'fruit production and causes severe losses.This study reported a high-quality‘Wushancuili'genome assembly consisting of a 302.17-Mb sequence with eight pseudo-chromosomes and a contig N50 of 23.59 Mb through the combination of Illumina sequencing,Pacific Biosciences HiFiⅢsequencing,and high-throughput chromosome conformation capture technology.A total of 25109 protein-coding genes are predicted and 54.17%of the genome is composed of repetitive sequences.‘Wushancuili'underwent a remarkable orthoselection during evolution.Gene identification revealed that loss-of-function in four core MYB10 genes results in the anthocyanin deficiency and absence of red color,revealing the green coloration due to the residual high chlorophyll in fruit skin.Besides,the occurrence of cracking is assumed to be closely associated with cell wall modification and frequently rain-induced pathogen enrichment through transcriptomic analysis.The loss of MYB10 genes might render fruit more susceptible to pathogen-mediated cracking by weakening the epidermal strength and reactive oxygen species(ROS)scavenging.Our findings provided fundamental knowledge regarding fruit coloration and rain-cracking and will facilitate genetic improvement and cultivation management in Chinese plums.

Myo-inositol mediates reactive oxygen species-induced programmed cell death via salicylic acid-dependent and ethylene-dependent pathways in apple

As a versatile compound,myo-inositol plays vital roles in plant biochemistry and physiology.We previously showed that exogenous application of myo-inositol had a positive role in salinity tolerance in Malus hupehensis Rehd.In this study,we used MdMIPS(the rate-limiting gene of myo-inositol biosynthesis)transgenic apple lines to gain new insights into the physiological role of myo-inositol in apple.Decreasing myo-inositol biosynthesis in apple lines by RNA silencing of MdMIPS1/2 led to extensive programmed cell death,which manifested as necrosis of both the leaves and roots and,ultimately,plant death.Necrosis was directly caused by the excessive accumulation of reactive oxygen species,which may be closely associated with the cell wall polysaccharide-mediated increase in salicylic acid and a compromised antioxidant system,and this process was enhanced by an increase in ethylene production.In addition,a high accumulation of sorbitol promoted necrosis.This synergetic interplay between salicylic acid and ethylene was further supported by the fact that increased myo-inositol accumulation significantly delayed leaf senescence in MdMIPS1-overexpressing apple lines.Taken together,our results indicated that apple myo-inositol regulates reactive oxygen species-induced programmed cell death through salicylic acid-dependent and ethylene-dependent pathways.