Samia Lotfy

A reference genetic map of C. clementina hort. ex Tan.; citrus evolution inferences from comparative mapping

BackgroundMost modern citrus cultivars have an interspecific origin. As a foundational step towards deciphering the interspecific genome structures, a reference whole genome sequence was produced by the International Citrus Genome Consortium from a haploid derived from Clementine mandarin. The availability of a saturated genetic map of Clementine was identified as an essential prerequisite to assist the whole genome sequence assembly. Clementine is believed to be a ‘Mediterranean’ mandarin × sweet orange hybrid, and sweet orange likely arose from interspecific hybridizations between mandarin and pummelo gene pools. The primary goals of the present study were to establish a Clementine reference map using codominant markers, and to perform comparative mapping of pummelo, sweet orange, and Clementine.ResultsFive parental genetic maps were established from three segregating populations, which were genotyped with Single Nucleotide Polymorphism (SNP), Simple Sequence Repeats (SSR) and Insertion-Deletion (Indel) markers. An initial medium density reference map (961 markers for 1084.1 cM) of the Clementine was established by combining male and female Clementine segregation data. This Clementine map was compared with two pummelo maps and a sweet orange map. The linear order of markers was highly conserved in the different species. However, significant differences in map size were observed, which suggests a variation in the recombination rates. Skewed segregations were much higher in the male than female Clementine mapping data. The mapping data confirmed that Clementine arose from hybridization between ‘Mediterranean’ mandarin and sweet orange. The results identified nine recombination break points for the sweet orange gamete that contributed to the Clementine genome.ConclusionsA reference genetic map of citrus, used to facilitate the chromosome assembly of the first citrus reference genome sequence, was established. The high conservation of marker order observed at the interspecific level should allow reasonable inferences of most citrus genome sequences by mapping next-generation sequencing (NGS) data in the reference genome sequence. The genome of the haploid Clementine used to establish the citrus reference genome sequence appears to have been inherited primarily from the ‘Mediterranean’ mandarin. The high frequency of skewed allelic segregations in the male Clementine data underline the probable extent of deviation from Mendelian segregation for characters controlled by heterozygous loci in male parents.

Characterization of microsatellite markers in mandarin orange (Citrus reticulata Blanco)

A dinucleotide‐enriched genomic library was obtained from mandarin orange (Citrus reticulata Blanco). A subset of 101 positive clones was sequenced and primers were designed. The loci were screened for levels of variation using 26–29 wild mandarin oranges collected in Vietnam. Forty‐three loci were polymorphic with the number of alleles ranging from two to 18. The observed heterozygosity (HO) and expected heterozygosity (HE) were from 0.03 to 0.96 and from 0.03 to 0.92, respectively.

Formation of ω-Feruloyloxypalmitic Acid and Tetradecyl Ferulate in Enzymic Extracts of Wound-Healing Potato Tuber Discs (Solanum tuberosum L.)

Suberin is a complex heteropolyrmer comprizing lipidic components attached to a phenolic matrix [1]. It naturally covers the underground parts of plants but it is also synthesized at the surface of wound-healing plant tissues. While the composition and the biosynthesis of the fatty acids and alcohols components of suberin have been extensively studied, very little is known about the composition and the enzymology of the phenolic fraction [1,2]. Soluble ferulic acid esters of saturated fatty alcohols, ranging in carbon chain length from C16 to C28, have been isolated from suberized potato periderm and it has been postulated that these alkyl ferulates could be suberin monomers [2,3]. We recently reported [4] the occurence in suberizing potato periderm (Solanum tuberosum L. cv Bintje) of a wound-induced acyl-CoA transferase catalysing the formation of ferulic acid esters of several mediumchain 1-alkanols and also, very efficiently, of ω-hydroxypalmitic acid (Fig. 1). It is the first time that an enzyme (HHT= hydroxycinnamoyl-CoA: Ωhydroxypalmitic acid O-hydroxycinnamoyltransferase) conjugating lipids to hydroxycinnamic acids is characterized.