Analysis Of Photosynthetic Characteristics And Leaves Proteome Of Wild Species And Cultivar Of Cassava

Cassava (Manihot esculenta Crantz) is an important source of food and biomass crops in the world, whose importance in tropical agriculture is next to rubber. As the signature crop in tropical agriculture economics, obtaining new varieties with high yield and high starch content is the goal of cassava breeding. And which greatly depend on the ability of photosynthesis, so enhancing photosynthetic efficiency certainly is an effective way for improving crop production.In this study, wild cassava (Manihot saxicola), wild relative W14(M. esculenta ssp. flabellifolia) and SC205(M. esculenta cv. SC No.205) differed in evolutionary position were used as materials. Leaf anatomical structures, diurnal changes of photosynthesis rate and chlorophyll fluorescence parameters were analyzed. Western blot was used to detect the expression level of Rubisco, PEPC, D1and OEC. Combining with leaf differential proteomics, the molecular mechanism of high photosynthetic efficiency in cassava was elaborated, which can provide theoretical support for selecting cassava varieties with high yield and high starch. The main results are as follows:1. Wild cassava (M. saxicola) and SC205belong to "special" C3plants, with "unique" green bundle sheath cell structure, but no typical kranz structure of C4plants. W14is in between of C3and C4plants whose development degree of green bundle sheath in leaves slightly lower. Although mesophyll cells are adjacent to the external of the green bundle sheath, they are arranged slightly loose.2. Chlorophyll content of wild cassava (M. saxicola), W14and SC205were positively correlated with photosynthetic rate, but the content of chlorophyll A and total chlorophyll in W14were significantly lower than wild cassava (M. saxicola) and SC205.3. In wild cassava (M. saxicola), W14and SC205, changes from7:00to17:00of chlorophyll fluorescence parameterφPPSⅡ showed a downward trend after it reached its summit at11:00. At this time point, the actual photosynthetic efficiency can be sequenced asφsc205>φwiid(M saxicola)>φw14.However, Fv/Fm in of W14was higher compared with wild cassava (M. saxicola) and SC205, indicating that W14might have a greater potential of photosynthetic capacity. The expression level changes of key proteins associated with photosynthesis (Rubisco, D1and OEC) in daytime also showed the trend of increasing first and followed decreasing. At11:00, the expression levels reached the highest expression level. But the expression of key enzyme PEPC in C4pathway in photosynthesis was not detected in wild cassava (M saxicola), W14and SC205.4. Compare with wild cassava (M. saxicola),8differential protein spots associated with photosynthesis in W14were down-regulated, while4proteins in SC205were up-regulated. These proteins are mainly belonging to Rubisco and RCA. Interaction of biological regulatory network models shows Rubisco and RCA is a key factor in network, in which,14-3-3protein as a signal transductor is closely linked of multiple metabolic pathways. Due to the high level expression of phosphoglycerate kinase in SC205leaves, as a signal,14-3-3promote protease expression associated with protein synthesis and starch synthesis, then induced high expression level of Rubisco and RCA, which improving the photosynthetic efficiency of cassava cultivar SC205.