Diversification of Genes Encoding Granule-Bound Starch Synthase in Monocots and Dicots Is Marked by Multiple Genome-Wide Duplication Events

Abstract

Starch is one of the major components of cereals, tubers, and fruits. Genes encoding granule-bound starch synthase (GBSS), which is responsible for amylose synthesis, have been extensively studied in cereals but little is known about them in fruits. Due to their low copy gene number, GBSS genes have been used to study plant phylogenetic and evolutionary relationships. In this study, GBSS genes have been isolated and characterized in three fruit trees, including apple, peach, and orange. Moreover, a comprehensive evolutionary study of GBSS genes has also been conducted between both monocots and eudicots. Results have revealed that genomic structures of GBSS genes in plants are conserved, suggesting they all have evolved from a common ancestor. In addition, the GBSS gene in an ancestral angiosperm must have undergone genome duplication ∼251 million years ago (MYA) to generate two families, GBSSI and GBSSII. Both GBSSI and GBSSII are found in monocots; however, GBSSI is absent in eudicots. The ancestral GBSSII must have undergone further divergence when monocots and eudicots split ∼165 MYA. This is consistent with expression profiles of GBSS genes, wherein these profiles are more similar to those of GBSSII in eudicots than to those of GBSSI genes in monocots. In dicots, GBSSII must have undergone further divergence when rosids and asterids split from each other ∼126 MYA. Taken together, these findings suggest that it is GBSSII rather than GBSSI of monocots that have orthologous relationships with GBSS genes of eudicots. Moreover, diversification of GBSS genes is mainly associated with genome-wide duplication events throughout the evolutionary course of history of monocots and eudicots.

Lineage-Specific Evolutionary Histories and Regulation of Major Starch Metabolism Genes during Banana Ripening

“…Palm and banana SSII genes might have been duplicated prior to Commelinid lineage divergence while grass GBSS could have originated from a monocot ancestral duplication ( Figures 3 and 4 ). The timing of monocot GBSSI/GBSSII duplication is unclear since our GBSS tree topology differed from previously published ones (Cheng et al, 2012) which suggested a shared ancestral GBSS duplication between eudicots and monocots thus predating eudicot/monocot split. The identification of eudicot GBSSII and GBSSI genes on grapevine syntenic blocks implies that they originated from the gamma hexaploidization (Jaillon et al, 2007) that is at the root of eudicot radiation.…”

“…SSI genes and homologs of the functional AtSS4 gene (SSIV) were mostly single copy in analyzed angiosperm species. The SSII and SSIII genes were found as single copy genes in sampled Eudicots but were duplicated in banana and also, as previously described, in grasses (Wu et al, 2008; Yan et al, 2009; Cheng et al, 2012). In addition, date palm SSII genes were also found duplicated ( Figure 4 ).…”

Identification and testing of reference genes for Sesame gene expression analysis by quantitative real-time PCR

“…GBSSI or waxy gene expresses exclusively in storage tissues such as seed endosperm and embryo, while the GBSSII gene is transcripted mainly in non-storage tissues such as leaf, stem, root, and pericarp (Dry et al 1992; Vrinten and Nakamura 2000; Dian et al 2003). In addition, other different isoforms of GBSS have also been reported in eudicot species (pea, orange, apple and peach), and have various expression profiles differing in cereals (Denyer et al 1997; Edwards et al 2002; Szydlowski et al 2011; Cheng et al 2012). While validating the normalized qRT-PCR system, we explored and confirmed the tissue specificity of SiSS gene in sesame.…”

Genetic diversity of Australian wild rice

“…This hypothesis is supported by evidence of common domestication alleles in both japonica and indica . The second theory proposes multiple independent domestications (Choi et al, 2017;Kumagai et al, 2016). This is attractive due to the significant genetic distance between japonica and indica clades estimated to be around 1 million years.…”

“…This is an area without a long history of rice cultivation, implying that the wild populations have remained largely isolated from the impacts of gene flow from domesticated crops that has apparently been widespread in Asia (Brozynska et al, 2017). The AA genome species of rice include cultivated species and their close relatives (Choi et al, 2017). Draft genome sequences of the AA genome populations from…”