Morphological Characteristics, Ultrastructure, and Chemical Constituents of the Endotesta in Ginkgo (Ginkgo biloba L.).

Ginkgo biloba L. is a tree species of significant economic and ecological importance. Prior studies of the Ginkgo biloba seed coat have predominantly focused on the sarcotesta and sclerotesta, with less attention paid to the endotesta. In this study, the development and formation of Ginkgo endotesta were examined using light microscopy and transmission electron microscopy. The structural properties of the mature endotesta were analyzed using micro-CT imaging and scanning electron microscopy. The results indicate that the endotesta possess a membranous structure primarily originating from the inner bead peridium, a segment of bead core tissue, and the macrospore membrane. The endotesta from the middle constriction line to the chalazal end comprises a single layer with a greyish-white papery structure. In contrast, the endotesta was divided into two inner and two outer layers, from the middle constriction line to the micropylar end. The outer endosperm adheres closely to the sclerotesta, while the inner endosperm adheres to the seed kernel. The surface of the endotesta was irregularly raised, with thicker wax at the chalazal end, whereas the micropylar end demonstrated similar characteristics with thinner wax and tumor layers. The endotesta contained 17 amino acids, 18 fatty acids, 10 trace elements, and 7 vitamins. Overall, its nutritional value was relatively well balanced.

Genetic diversity, population structure, and genome-wide association analysis of ginkgo cultivars.

Ginkgo biloba is an economically valuable tree worldwide. The species has nearly become extinct during the Quaternary, which has likely resulted in reduction of its genetic variability. The genetic variability is now conserved in few natural populations in China and a number of cultivars that are, however, derived from a few ancient trees, helping the species survive in China through medieval times. Despite the recent interest in ginkgo, however, detailed knowledge of its genetic diversity, conserved in cultivated trees and cultivars, has remained poor. This limits efficient conservation of its diversity as well as efficient use of the existing germplasm resources. Here we performed genotyping-by-sequencing (GBS) on 102 cultivated germplasms of ginkgo collected to explore their genetic structure, kinship, and inbreeding prediction. For the first time in ginkgo, a genome-wide association analysis study (GWAS) was used to attempt gene mapping of seed traits. The results showed that most of the germplasms did not show any obvious genetic relationship. The size of the ginkgo germplasm population expanded significantly around 1500 years ago during the Sui and Tang dynasties. Classification of seed cultivars based on a phylogenetic perspective does not support the current classification criteria based on phenotype. Twenty-four candidate genes were localized after performing GWAS on the seed traits. Overall, this study reveals the genetic basis of ginkgo seed traits and provides insights into its cultivation history. These findings will facilitate the conservation and utilization of the domesticated germplasms of this living fossil plant.

High-Depth Transcriptome Reveals Differences in Natural Haploid Ginkgo biloba L. Due to the Effect of Reduced Gene Dosage.

As a representative of gymnosperms, the discovery of natural haploids of Ginkgo biloba L. has opened a new door for its research. Haploid germplasm has always been a research material of interest to researchers because of its special characteristics. However, we do not yet know the special features and mechanisms of haploid ginkgo following this significant discovery. In this study, we conducted a homogenous garden experiment on haploid and diploid ginkgo to explore the differences in growth, physiology and biochemistry between the two. Additionally, a high-depth transcriptome database of both was established to reveal their transcriptional differences. The results showed that haploid ginkgo exhibited weaker growth potential, lower photosynthesis and flavonoid accumulation capacity. Although the up-regulated expression of DEGs in haploid ginkgo reached 46.7% of the total DEGs in the whole transcriptome data, the gene sets of photosynthesis metabolic, glycolysis/gluconeogenesis and flavonoid biosynthesis pathways, which were significantly related to these differences, were found to show a significant down-regulated expression trend by gene set enrichment analysis (GSEA). We further found that the major metabolic pathways in the haploid ginkgo transcriptional database were down-regulated in expression compared to the diploid. This study reveals for the first time the phenotypic, growth and physiological differences in haploid ginkgos, and demonstrates their transcriptional patterns based on high-depth transcriptomic data, laying the foundation for subsequent in-depth studies of haploid ginkgos.