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Sucrose, an important sugar, is transported from source to sink tissues through the phloem, and plays important role in the development of important traits in plants. However, the SUT gene family is still not well characterized in pomegranate. In this study, we first identified the pomegranate sucrose transporter ( SUT) gene family from the whole genome. Then, the phylogenetic relationship of SUT genes, gene structure and their promoters were analyzed. Additionally, their expression patterns were detected during the development of the seed. Lastly, genetic transformation and cytological observation were used to study the function of PgL0145810.1 . A total of ten pomegranate SUT genes were identified from the whole genome of pomegranate 'Tunisia'. The promoter region of all the pomegranate SUT genes contained myeloblastosis (MYB) elements. Four of the SUT genes, PgL0328370.1 , PgL0099690.1 , PgL0145810.1 and PgL0145770.1 , were differentially expressed during seed development. We further noticed that PgL0145810.1 was expressed most prominently in the stem parts in transgenic plants compared to other tissue parts (leaves, flowers and silique). The cells in the xylem vessels were small and lignin content was lower in the transgenic plants as compared to wild Arabidopsis plants. In general, our result suggests that the MYB cis-elements in the promoter region might regulate PgL0145810.1 expression to control the structure of xylem, thereby affecting seed hardness in pomegranate.

Complete and highly accurate reference genomes and gene annotations are indispensable for basic biological research and trait improvement of woody tree species. In this study, we integrated single-molecule sequencing and high-throughput chromosome conformation capture techniques to produce a high-quality and long-range contiguity chromosome-scale genome assembly of the soft-seeded pomegranate cultivar 'Tunisia'. The genome covers 320.31 Mb (scaffold N50 = 39.96 Mb; contig N50 = 4.49 Mb) and includes 33 594 protein-coding genes. We also resequenced 26 pomegranate varieties that varied regarding seed hardness. Comparative genomic analyses revealed many genetic differences between soft- and hard-seeded pomegranate varieties. A set of selective loci containing SUC8-like, SUC6, FoxO and MAPK were identified by the selective sweep analysis between hard- and soft-seeded populations. An exceptionally large selective region (26.2 Mb) was identified on chromosome 1. Our assembled pomegranate genome is more complete than other currently available genome assemblies. Our results indicate that genomic variations and selective genes may have contributed to the genetic divergence between soft- and hard-seeded pomegranate varieties., (© 2019 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

The pomegranate, Punica granatum L., which has been cultivated since antiquity, is known to be a superfruit, possessing an array of functional anti-oxidants and various other health benefits. The hardness of pomegranate seeds is an important indicator of fruit quality, which in turn affects economic value and market demand. However, the molecular mechanism underlying pomegranate seed hardness remains to be fully understood. In this study, we found a positive correlation between seed hardness and lignin content in two pomegranate varieties: "Tunisia" and "Sanbai". Specifically, genes associated with lignin biosynthesis were differentially expressed in soft-seed and hard-seed pomegranate varieties. Among these differential genes, we cloned and characterized the NAC transcription factor PgSND1-like. Sequence alignment found a single base replacement at the 166-bp position of CDS in the PgSND1-like gene from "Tunisia" and "Sanbai". Both PgSND1-like (Sanbai) and PgSND1-like (Tunisia) proteins are localized in the cell nucleus and have a transcription activation domain in the C-terminus. Yeast two-hybrid analysis indicated that PgSND1-like protein interacts with itself to form a homodimer. Overexpression of PgSND1-like (Sanbai) in Arabidopsis showed a higher lignin content in inflorescence stem and mature seed compared with wild-type Arabidopsis. Accordingly, the expression levels of several lignin biosynthesis-associated genes were upregulated in stem cells and mature seeds of transgenic plants. However, PgSND1-like (Tunisia) transgenic Arabidopsis showed no phenotypic differences with wild-type Arabidopsis. Taken together, we suggest that PgSND1-like may regulate at least two different functions in two pomegranate varieties, promoting lignin biosynthesis and seed hardness of pomegranate., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

The breeding of new soft-seeded pomegranate cultivars provides new products for the market and increases farmers' incomes, yet the genetic architecture mediating seed hardness is largely unknown. Here, the seed hardness and hundred-seed weights of 26 cultivars were determined in 2 successive years. We conducted miRNA and mRNA sequencing to analyse the seeds of two varieties of Punica granatum: soft-seeded Tunisia and hard-seeded Sanbai, at 60 and 120 d after flowering. Seed hardness was strongly positively correlated with hundred-seed weight. We detected 25 and 12 differentially expressed miRNA-mRNA pairs with negative regulatory relationships between the two genotypes at 60 and 120 d after flowering, respectively. These miRNA-mRNA pairs mainly regulated seed hardness by altering cell wall structure. Transcription factors including NAC1, WRKY and MYC, which are involved in seed hardness, were targeted by differentially expressed mdm-miR164e and mdm-miR172b. Thus, seed hardness is the result of a complex biological process regulated by a miRNA-mRNA network in pomegranate. These results will help us understand the complexity of seed hardness and help to elucidate the miRNA-mediated molecular mechanisms that contribute to seed hardness in pomegranate.

Pomegranate (Punica granatum L.) belongs to Punicaceae, and is valued for its social, ecological, economic, and aesthetic values, as well as more recently for its health benefits. The ‘Tunisia’ variety has softer seeds and big arils that are easily swallowed. It is a widely popular fruit; however, the molecular mechanisms of the formation of hard and soft seeds is not yet clear. We conducted a de novo assembly of the seed transcriptome in P. granatum L. and revealed differential gene expression between the soft-seed and hard-seed pomegranate varieties. A total of 35.1 Gb of data were acquired in this study, including 280,881,106 raw reads. Additionally, de novo transcriptome assembly generated 132,287 transcripts and 105,743 representative unigenes; approximately 13,805 unigenes (37.7%) were longer than 1,000 bp. Using bioinformatics annotation libraries, a total of 76,806 unigenes were annotated and, among the high-quality reads, 72.63% had at least one significant match to an existing gene model. Gene expression and differentially expressed genes were analyzed. The seed formation of the two pomegranate cultivars involves lignin biosynthesis and metabolism, including some genes encoding laccase and peroxidase, WRKY, MYB, and NAC transcription factors. In the hard-seed pomegranate, lignin-related genes and cellulose synthesis-related genes were highly expressed; in soft-seed pomegranates, expression of genes related to flavonoids and programmed cell death was slightly higher. We validated selection of the identified genes using qRT-PCR. This is the first transcriptome analysis of P. granatum L. This transcription sequencing greatly enriched the pomegranate molecular database, and the high-quality SSRs generated in this study will aid the gene cloning from pomegranate in the future. It provides important insights into the molecular mechanisms underlying the formation of soft seeds in pomegranate. [ABSTRACT FROM AUTHOR]