Abstract
BackgroundCassava (Manihot esculenta Crantz) is an important food crop known for its high starch content. Polyploid breeding is effective in its genetic improvement, and use of 2n gametes in sexual polyploid breeding is one of the potential methods for cassava breeding and improvement. In our study, the cassava sexual tetraploid (ST), which carries numerous valuable traits, was successfully generated by hybridizing 2n female gametes SC5 (♀) and 2n male gametes SC10 (♂). However, the molecular mechanisms remain unclear. To understand these underlying molecular mechanisms behind the phenotypic alterations and heterosis in ST plants, we investigated the differences in gene expression between polyploids and diploids by determining the transcriptomes of the ST plant and its parents during the tuber root enlargement period. We also compared the characters and transcriptomes of the ST plant with its parents.ResultsThe ST plant was superior in plant height, stem diameter, leaf area, petiole length, plant weight, and root weight than the parent plants, except the leaf number, which was lower. The number of starch granules was higher in the roots of ST plants than those in the parent plants after five months (tuber root enlargement period), which could be due to a higher leaf net photosynthetic rate leading to early filling of starch granules. Based on transcriptome analysis, we identified 2934 and 3171 differentially expressed genes (DEGs) in the ST plant as compared to its female and male parents, respectively. Pathway enrichment analyses revealed that flavonoid biosynthesis and glycolysis/gluconeogenesis were significantly enriched in the ST plants, which might contribute to the colors of petiole (purple-red), root epidermis (dark brown), and tuber starch accumulation, respectively.ConclusionsAfter sexual polyploidization, the phenotype of ST has changed significantly in comparison to their diploid parents, mainly manifest as enlarged biomass, yield, early starch filling, deep colored petiole and root epidermis. The tetraploid plants were also mature early due to early starch grain filling. Owing to enriched flavonoid biosynthesis and glycolysis/gluconeogenesis, they are possibly resistant to adversity stresses and provide better yield, respectively.
Highlights
Cassava (Manihot esculenta Crantz) is an important food crop known for its high starch content
The results show that the ploidy of cassava sexual tetraploids (ST) is uniform and stable (Fig. 1e, f)
The present study investigated the characters and genome-wide gene expression profiling of cassava sexual tetraploid and its diploid parents, with an aim to illustrate the molecular mechanisms of character changes after sexual polyploidization
Summary
Cassava (Manihot esculenta Crantz) is an important food crop known for its high starch content. To understand these underlying molecular mechanisms behind the phenotypic alterations and heterosis in ST plants, we investigated the differences in gene expression between polyploids and diploids by determining the transcriptomes of the ST plant and its parents during the tuber root enlargement period. Cassava (Manihot esculenta Crantz) is the fourth most widely grown crop in the tropics, one of three major starch crops in the world, and the main food crop in tropical Africa [1]. Its tuberous roots are rich in starch— 20 - 40% of fresh weight and 80% of dry weight, — giving it the highest rank among the known starch crops, and cassava is often known as “underground food”, “king of starch”, “special crop” and “energy crop” [2,3,4]. The traditional improvement approach has helped cassava breeding process, it is still far from enough to meet the demand for cassava root yield, starch content, and resistance to abiotic and biotic stresses
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