The Molecular Mechanism On The Improved Photosynthetic Capacity Of Hickory Pericarp By Cross-pollination

Hickory(Carya cathayensis Sarg.)and pecan(C.illinoensis K.Koch)are the trees widely planted in the world.The pericarp becomes green,the dry matter of fruit and kernel significantly increased,the average weight of single fruit increased by 39.1% after pollinated by pecan pollen.Previously,it has been confirmed by the molecular marker and anatomy that the enlargement of the fruits which are pollinated by pecan is not due to the change of genetic material.Therefore,it is of great significance to explore the mechanism of xenia in hickory.The substances require for the growth and development of fruit are mainly derived from the photosynthesis of green organs,beyond that,non-leaf organs also have a complete chloroplast structure,which is an important supplementary source of fruits.Because of the significantly improvement of the photosynthetic capacity and the light-resistance after pollinated by pecan pollen,we focus on the differences in photosynthethesis-related genes,and try to reveal the molecular mechanism of photosynthesis by the comparative transcriptome analysis of the pericarps which are pollinated by two different pollens during the fruit development periods.The main results are following:(1)65-108 days after pollinated(65DAP-108DAP),the pecan pollinated(pp)fruits were significantly larger than the hickory pollinated fruits(hp).After wrapping the fruits with dichlorophenyl dimethylures(inhibitory effect is about 50%),we found the fresh matter,dry matter and the oil content of the fruit pollinated by hickory decreased by 10.2%,10%and 7.5% respectively,and of the fruit pollinated by pecan decreased by 16%,28.3% and5.1% respectively.The result showed that the photosynthesis of fruit played an important role in hickory fruit development.(2)At 15 DAP,686 differentially expressed genes were found,405 genes were significantly up-regulated after pecan pollinated.GO analysis showed the differential genes were mainly involved in glucose metabolism and protein phosphorylation,tetrapyrrole binding protein,hydrolase activity,catalytic activity related.KEGG analysis showed that genes were mainly enriched in the synthesis and metabolism of phenyl propane,plant hormone signal transduction,and alkaloid synthesis.At 30 DAP,2367differentially expressed genes were found,982 genes were significantly up-regulated after pecan pollinted and 1385 were significantly down-regulated.The GO analysis showed that the differential genes were mainly involved in carbon metabolism,carbohydrate synthesis,photosynthesis,photosystem I and the reaction centers,photosynthetic membranes,and partial transferase activities.KEGG analysis showed that the differential pathways were mainly plant hormone signal transduction,photosynthesis-absorption protein,and amino acid metabolism.At 65 DAP,1984 differential genes were found,691 genes were up-regulated and 1293 genes were down-regulated.The GO and KEGG annotation analysis showed that the differential genes were mainly related to the metabolism,regulation,catalytic activity,ion binding,and glucose metabolism of organic matter.The DEGs involved in 113 pathways,such as plant pathogen interaction,photosynthetic light-harvesting proteins,and plant hormone signal transduction and so on.At 65 DAP,the chlorophyll synthesis,light capture,and carbon assimilation were all found significantly different.According to transcriptome analysis,we found the gene expression was significantly different at 15 DAP after pollinated with different pollen,but there was no significant difference in the photosynthetic pathway.When the development continued until 30 DAP,the chlorophyll synthesis pathway,light-capturing protein and other photosynthetic pathways were found significantly different,besides,the carbon fixation were also significantly different at 65 DAP So it is conferred that the enhanced photosynthetic ability may be caused by some signal released by pecan pollen.(3)At 30 DAP,the genes involved in the pathway of porphyrin and chlorophyll metabolism were significantly up-regulated after pecan pollinated,such as chlorophyllase(CLH),magnesium-protoporphine cyclase(CRD),heme oxygenase(HEMA),Deesterification chlorophyll oxygenase(CAO),chlorophyll synthase(CLHG)and so on which might lead to the higher chlorophyll content of pericarp.The expression of light-harvesting protein(LHCII),light-repair related proteins and 32 heat shock proteins(HSP),Rubisco activase(RCA),carbonic anhydrase(CA)were significantly up-regulated after pecan pollinated at 65 DAP.From 55 DAP to 85 DAP,the chlorophyll content,net photosynthetic rate,and Rubisco activity were higher in pecan pollinated fruits than that in hickory pollinated fruits.It can be seen that during the rapid development period of hickory fruit,the higher capacity of photosynthetic and chlorophyll synthesis,the more carbon sources hickory fruits have.