Cassava,a tropical food,feed and biofuel crop,has great capacity for biomass accumulation and an extraordinary efficiency in water use and mineral nutrition,which makes it highly suitable as a model plant for tropical crops.However,the understanding of the metabolism and genomics of this important crop is limited.The recent breakthroughs in the genomics of cassava,including whole-genome sequencing and transcriptome analysis,as well as advances in the biology of photosynthesis,starch biosynthesis,adaptation to drought and high temperature,and resistance to virus and bacterial diseases,are reviewed here.Many of the new developments have come from comparative analyses between a wild ancestor and existing cultivars.Finally,the current challenges and future potential of cassava as a model plant are discussed.
Shengkui ZHANGPing’an MAHaiyan WANGCheng LUXin CHENZhiqiang XIAMeiling ZOUXinchen ZHOUWenquan WANG
Cassava is a staple food, feed and bioenergy crop important to the world especially in the tropics.Domesticated cassava is characterized by powerful carbohydrate accumulation but its wild progenitor is not.Here, we investigated the transcriptional differences of eight c DNA libraries derived from developing leaf, stem and storage root of cassava cv. Arg7 and an ancestor line,W14, using next generation sequencing system. A total of41302 assembled transcripts were obtained and from these,25961 transcripts with FPKM≥3 in at least one library were named the expressed genes. A total of 2117, 1963 and3584 transcripts were found to be differentially expressed in leaf, stem and storage root(150 d after planting),respectively, between Arg7 and W14 and ascribed to 103,93 and 119 important pathways in leaf, stem and storage root, respectively. The highlight of this work is that the genes involved in light response, such as those for photosystem I(PSA) and photosystem II(PSB), other genes involved in light harvesting, and some of the genes in the Calvin cycle of carbon fixation were specially upregulated in leaf. Genes for transport and also for key rate-limiting enzymes(PFK, PGK and PK, GAPDH)coupling ATP consumption in glycolysis pathway were predominantly expressed in stem, and genes for sucrose degradation(INVs), amylose synthesis(GBSS) and hydrolysis(RCP1, AMYs), the three key steps of starch metabolism, and transport associated with energy translocation(ABC, AVPs and ATPase) and their upstream transcription factors had enhanced expression in storage root in domesticated cassava. Co-expression networks among the pathways in each organs revealed therelationship of the genes involved, and uncovered some of the important hub genes and transcription factors targeting genes for photosynthesis, transportation and starch biosynthesis.
