Abstract
Cassava polyploid breeding has drastically improved our knowledge on increasing root yield and its significant tolerance to stresses. In polyploid cassava plants, increases in DNA content highly affect cell volumes and anatomical structures. However, the mechanism of this effect is poorly understood. The purpose of the present study was to compare and validate the changes between cassava cultivar NZ199 diploid and autotetraploid at proteomic levels. The results showed that leaf proteome of cassava cultivar NZ199 diploid was clearly differentiated from its autotetraploid genotype using 2-DE combined MS technique. Sixty-five differential protein spots were seen in 2-DE image of autotetraploid genotype in comparison with that of diploid. Fifty-two proteins were identified by MALDI-TOF-MS/MS, of which 47 were up-regulated and 5 were down-regulated in autotetraploid genotype compared with diploid genotype. The classified functions of 32 up-regulated proteins were associated with photosynthesis, defense system, hydrocyanic acid (HCN) metabolism, protein biosynthesis, chaperones, amino acid metabolism and signal transduction. The remarkable variation in photosynthetic activity, HCN content and resistance to salt stress between diploid and autotetraploid genotypes is closely linked with expression levels of proteomic profiles. The analysis of protein interaction networks indicated there are direct interactions between the 15 up-regulation proteins involved in the pathways described above. This work provides an insight into understanding the protein regulation mechanism of cassava polyploid genotype, and gives a clue to improve cassava polyploidy breeding in increasing photosynthesis and resistance efficiencies.
Highlights
Cassava (Manihot esculenta Crantz) is a perennial shrub of the Euphorbiaceae family
Examination using the leaves of confirmed diploid (Fig. 1A and C) and autotetraploid (Fig. 1B and D) cassava NZ199 plants showed that the chromosome number from diploid genotype was 36 (2n = 2x = 36) (Fig. 1E), whereas that of autotetraploid genotype was 72 (4n = 4x = 72) (Fig. 1F)
Using a spot-to-spot comparison and statistical analysis, a total of 65 stained spots (Fig. 2C) from autotetraploid genotype were found to have significant changes (p,0.05) with greater than 2.0-fold altered intensity compared with diploid genotype
Summary
Cassava (Manihot esculenta Crantz) is a perennial shrub of the Euphorbiaceae family. It is a major calorie source for sub-Saharan Africans and is ranked the sixth most important source of calorie in human diet worldwide [1]. Cassava breeding faces several limitations such as (1) its heterozygous genetic makeup which makes it time consuming to breed efficiently and (2) low tolerance to salinity and cold which makes it difficult to grow in north China and saline soils [3]. A draft genome sequence and limited proteome identification have been generated to provide new clues for cassava breeders to overcome the limitations [3,4,5,6]
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