Molecular cloning, characterization and expression analysis of three key starch synthesis-related genes from the bulb of a rare lily germplasm, Lilium brownii var. giganteum.

Abstract

Starch is the predominant compound in bulb scales, and previous studies have shown that bulblet development is closely associated with starch enrichment. However, how starch synthesis affects bulbification at the molecular level is unclear. In this study, we demonstrate that Lilium brownii var. giganteum, a wild lily with a giant bulb in nature, and L. brownii, the native species, have different starch levels and characteristics according to cytological and ultra-structural observations. We cloned the complete sequence of three key gene-encoding enzymes (LbgAGPS, LbgGBSS, andLbgSSIII) during starch synthesis by rapid amplification of 5' and 3' complementary DNA (cDNA) ends (RACE) technology. Bioinformatics analysis revealed that the proteins deduced by these genes contain the canonical conserved domains. Constructed phylogenetic trees confirmed the evolutionary relationships with proteins from other species, including monocotyledons and dicotyledons. The transcript levels of various tissues and time course samples obtained during bulblet development uncovered relatively high expression levels in bulblets and gradual increase expression accompanying bulblet growth. Moreover, a set of single nucleotide polymorphisms (SNPs) was discovered in the AGPS genes of four lily genotypes, and a purifying selection fashion was predicted according to the non-synonymous/synonymous (Ka/Ks) values. Taken together, our results suggested that key starch-synthesizing genes might play important roles in bulblet development and lead to distinctive phenotypes in bulblet size.