SummaryPomegranate (Punica granatum L.) has an ancient cultivation history and has become an emerging profitable fruit crop due to its attractive features such as the bright red appearance and the high abundance of medicinally valuable ellagitannin‐based compounds in its peel and aril. However, the limited genomic resources have restricted further elucidation of genetics and evolution of these interesting traits. Here, we report a 274‐Mb high‐quality draft pomegranate genome sequence, which covers approximately 81.5% of the estimated 336‐Mb genome, consists of 2177 scaffolds with an N50 size of 1.7 Mb and contains 30 903 genes. Phylogenomic analysis supported that pomegranate belongs to the Lythraceae family rather than the monogeneric Punicaceae family, and comparative analyses showed that pomegranate and Eucalyptus grandis share the paleotetraploidy event. Integrated genomic and transcriptomic analyses provided insights into the molecular mechanisms underlying the biosynthesis of ellagitannin‐based compounds, the colour formation in both peels and arils during pomegranate fruit development, and the unique ovule development processes that are characteristic of pomegranate. This genome sequence provides an important resource to expand our understanding of some unique biological processes and to facilitate both comparative biology studies and crop breeding.

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Pomegranate (Punica granatum L.) is widely grown in arid and semiarid regions, where the salinization may have developed through irrigation. A greenhouse experiment was conducted to investigate NaCl stress on growth, photosynthesis, and nutrients of 18 pomegranate cultivars. One group was irrigated twice a week with a nutrient solution. The other group was watered twice a week with the same nutrient solution and 200 mM NaCl for five weeks. Dry weight, shoot length, new shoot number, root length and number, leaf area, leaf relative water content, and net photosynthesis of salt-treated plants were negatively impacted by salt stress, and there was a significant difference among cultivars. Few foliar damages were observed. Na content of plants significantly increased in all cultivars, while P, S, K, Ca, Mg, Si, Al, Zn content of plants decreased under salt stress. Fe, Mn, and Cu content increased in most cultivars. Pomegranate accumulated supraoptimal Na mostly in roots and transported more K and Ca to shoots, which was attributed to maintaining a higher ratio of K/Na and Ca/Na in the aerial part of plants. Ten of the 18 cultivars were considered salt-tolerant, which would offer a reference for pomegranate cultivation on saline lands.

Pomegranates (Punica granatum L.) are one of the most popular fruit trees cultivated in arid and semi-arid tropics and subtropics. In this study, we determined and characterized three complete chloroplast (cp) genomes of P. granatum cultivars with different phenotypes using the genome skimming approach. The complete cp genomes of three pomegranate cultivars displayed the typical quadripartite structure of angiosperms, and their length ranged from 156,638 to 156,639 bp. They encoded 113 unique genes and 17 are duplicated in the inverted regions. We analyzed the sequence diversity of pomegranate cp genomes coupled with two previous reports. The results showed that the sequence diversity is extremely low and no informative sites were detected, which suggests that cp genome sequences may be not be suitable for investigating the genetic diversity of pomegranate genotypes. Further, we analyzed the codon usage pattern and identified the potential RNA editing sites. A comparative cp genome analysis with other species within Lythraceae revealed that the gene content and organization are highly conserved. Based on a site-specific model, 11 genes with positively selected sites were detected, and most of them were photosynthesis-related genes and genetic system-related genes. Together with previously released cp genomes of the order Myrtales, we determined the taxonomic position of P. granatum based on the complete chloroplast genomes. Phylogenetic analysis suggested that P. granatum form a single clade with other species from Lythraceae with a high support value. The complete cp genomes provides valuable information for understanding the phylogenetic position of P. gramatum in the order Myrtales.

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Exterior fruit color is an important trait for the evaluation of pomegranate fruit quality, but the molecular mechanism underlying the variation in color between red- and white-fruited pomegranate is poorly understood. In this study, full-length cDNA clones encoding enzymes involved in anthocyanin biosynthesis-such as chalcone synthase, chalcone isomerase, flavanone 3-hydoxylase, dihydroflavonol 4-reductase, anthocyanidin synthase (ANS), UDP-glucose-flavonoid 3-O-glucosyltransferase, and the R2R3 MYB transcription factor PgMYB-were isolated from fruit peels. In addition, transcript levels of anthocyanin biosynthetic genes were quantitatively measured by real-time PCR in red and white fruits. In both cultivars, two expression peaks for structural genes were detected during fruit development, whereas only one peak was observed-during early development-for PgMYB. While PgMYB is important for flavonoid biosynthesis, other transcription factors appear to also be necessary for the regulation of anthocyanin biosynthesis. No anthocyanins were detected in the white cultivar. Peels of white fruits contained transcripts of all identified genes except for PgANS, suggesting that the lack of PgANS expression may be the main factor responsible for the absence of anthocyanins in white pomegranate. PgANS may be the key gene involved in anthocyanin biosynthesis in pomegranate fruit.

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