| Phosphorus is a major nutrient element with low availability,which is necessary for plant growth and development,as well as for crop yield and ecosystem productivity.Citrus is an evergreen broad-leaved fruit tree including numerous species and cultivars with an extensive global planting area.In this study,two late-maturing citrus cultivars and two mid-maturing citrus cultivars were selected to determine the photosynthetic parameters and phosphorus-based biochemical indexes in four important developmental stages.By using the method of comparison among cultivars,the seasonal patterns of photosynthetic parameters in the leaves of different citrus cultivars and the seasonal change patterns of different components of phosphorus in leaves and roots were compared.the main purpose is to explore the seasonal pattern of phosphorus in citrus leaves and roots,as well as the relationship between seasonal patterns,cultivars and fruit ripening period.Finally,based on the transcriptome data,the gene co-expression network associated with phosphorus-related physiological traits(total phosphorus(total P),inorganic phosphorus(P_i)and acid phosphatase(ACP)in citrus leaves and roots was constructed by WGCNA,which mainly identified the gene co-expression modules related to total P,P_i and ACP,and found out the key candidate genes related to phosphorus.Then the key genes were analyzed and annotated by GO and KEGG.To explore the main functions and expression pathways of key phosphorus-related genes in citrus.The main results are as follows:(1)The results showed that the seasonal changes of leaf photosynthetic parameters of all citrus cultivars were similar in the whole experimental cycle.The seasonal changes of net photosynthetic rate,stomatal conductance and transpiration rate in leaves were very significant,especially in July,the net photosynthetic rate,stomatal conductance and transpiration rate of all citrus cultivars reached the highest peak.In addition,the results showed that except for intercellular carbon dioxide concentration,net photosynthetic rate,stomatal conductance and transpiration rate were significantly different among cultivars at different developmental stages,especially during fruit ripening period.the net photosynthetic rate of late-maturing cultivars in December was significantly higher than that of middle-maturing cultivars.(2)The results showed that during the whole experimental cycle,the seasonal patterns of total carbon(total C)content in leaves and roots of all citrus cultivars were similar and stable,and the differences among cultivars were not significant.Compared with total C,the contents of total nitrogen(total N)and total P varied greatly in seasons,and the overall change trend was almost opposite,and there were significant differences among cultivars.In addition,the results also showed that the seasonal changes of moisture content,P_i,ACP,C/N ratio,C/P ratio and N/P ratio in leaves of all citrus cultivars were significantly higher than those in roots,and there were significant differences among cultivars at different developmental stages.Especially during fruit ripening,the difference of nutrient elements between middle-maturing cultivars and late-maturing cultivars was the most significant.(3)The results showed that through WGCNA analysis of 8982 expressed genes in leaves and 5508 expressed genes in roots,citrus leaves were divided into 14 modules,of which the most valuable module related to total P and P_i was blue module,with 4727genes,and the most valuable module related to ACP was violet module,with 308 genes.Citrus roots are divided into 11 modules,among which the most valuable module related to total P and P_i is brown module,which has 739 genes,and the most valuable module related to ACP in roots is lightcyan module,which has 1818 genes.After screening hub genes,873 hub genes were screened from leaf total P and P_i related blue modules,9 hub genes were screened from ACP related violet modules,34 hub genes were screened from total P and P_i related brown modules in roots,and 5 hub genes were screened from ACP related lightcyan modules.Finally,the selected hub genes were annotated and enriched by GO and KEGG.The hub genes of phosphorus in leaves and roots were mainly annotated in biosynthesis,metabolic pathway and cell composition,mainly enriched in carbohydrate synthesis,fatty acid synthesis,amino acid synthesis,catalytic regulation and redox pathway.To sum up,in the whole experimental cycle,except intercellular carbon dioxide,the photosynthetic parameters of the four cultivars of citrus leaves had a common seasonal change pattern,and there were significant differences among cultivars.The seasonal change patterns of total P and P_i in leaves and roots of the four cultivars were significantly different,especially in the fruit ripening stage.The key genes related to phosphorus in citrus leaves and roots are mainly concentrated in carbohydrate synthesis,fatty acid synthesis,amino acid synthesis,catalytic regulation and redox pathway. |
