Abstract
Litchi chinensis is a subtropical fruit crop, popular for its nutritional value and taste. Fruits with small seed size and thick aril are desirable in litchi. To gain molecular insight into gene expression that leads to the reduction in the size of seed in Litchi chinensis, transcriptomes of two genetically closely related genotypes, with contrasting seed size were compared in developing ovules. The cDNA library constructed from early developmental stages of ovules (0, 6, and 14 days after anthesis) of bold- and small-seeded litchi genotypes yielded 303,778,968 high quality paired-end reads. These were de-novo assembled into 1,19,939 transcripts with an average length of 865 bp. A total of 10,186 transcripts with contrast in expression were identified in developing ovules between the small- and large- seeded genotypes. A majority of these differences were present in ovules before anthesis, thus suggesting the role of maternal factors in seed development. A number of transcripts indicative of metabolic stress, expressed at higher level in the small seeded genotype. Several differentially expressed transcripts identified in such ovules showed homology with Arabidopsis genes associated with different stages of ovule development and embryogenesis.
Highlights
Litchi chinensis is a subtropical fruit crop, popular for its nutritional value and taste
Highest homology was noticed with transcripts from Fragaria vesca (39.31%), followed by Citrus sinensis (38.90%), Populus trichocarpa (38.73%), Ricinus communis (38.25%) and Vitis vinifera (38.10%) (Supplementary Table S2)
A total of 68,988 (57.51%) transcripts, including their possible splice variants, showed no homology with any of the eight species, NR and Swiss-Prot databases examined in the study
Summary
Several transcripts which showed no expression in the ovule of bold-seeded genotype were significantly expressed in small-seeded litchi and were homologous to stress related genes at 0 DAA (Supplementary Table S4). EP3 chitinase (AT3G54420; c45503_g1_i1 & c45503_g1_i2) and phytosulfokine 2/PSK2 (AT2G22860; c79596_g1_i1) hamper embryo development by inducing somatic embryogenesis[74] These genes showed higher expression in small-seeded litchi genotype at 0 DAA (Supplementary Table S3). Our analysis shows that the genes involved in endosperm development as well as embryo development were associated with small seed size in the small-seeded genotype of litchi Such genes were related to hormone biosynthesis pathways, transcription factors, ovule identity determinants, and embryogenesis. A number of genes expressed differentially at 0 DAA, suggesting that some factors resident in maternal tissue may set in the process that leads to the reduced seed size in the small-seeded litchi genotypes
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