The Function Of POLGAMMA2 And ChlH Gene In The Formation Of Yellow Leaves Of Forsythia

The leaves of Forsythia are yellow,and they have high ornamental value.They can also be used for garden planting and urban greening.Our research group has sorted out 7 genes related to the yellow leaves of Forsythia through transcriptome data analysis,and verified their function by using the VIGS gene silencing technology of Forsythia,screening out two key genes Chl H and POLGAMMA2,that were associated with yellow leaves.However,gene function verification of Chl H and POLGAMMA2 is not complete,and the molecular regulation mechanism of Chl H and POLGAMMA2 is unclear.This research verified Chl H and POLGAMMA2 genes’ function in the formation of Forsythia’s yellow leaves through VIGS verification,population verification,transcriptome analysis and transient overexpression verification.The main conclusions are as follow:(1)The q RT-PCR method was used to determine the expression level of Chl H and POLGAMMA2 genes in the four groups of Forsythia(light yellow,dark yellow,light green and dark green),combined with the physiological data results.It was found that the color of Forsythia leaves was green when the Chl H and POLGAMMA2 genes were expressed at high level,while the color of Forsythia leaves was yellow when these two genes were expressed at low level.The expression level of these two genes in green leaves was twice than that of yellow leaves,and the content of chlorophyll and carotenoid was 3times than that of yellow leaves.(2)Using VIGS technology to silence Chl H and POLGAMMA2 genes in tobacco and tomato respectively.It was found that the silencing of Chl H could reduce the chlorophyll content by 70%,which inhibited the synthesis of chlorophyll,so that the plant leaves changed from green to yellow.After POLGAMMA2 was silenced,the chlorophyll content was reduced by 80%,and the leaves turned white.The silence of this gene had a strong impact on the completion of chloroplast structure,reducing the chlorophyll content.And finally it had influence on leaf color.(3)Agrobacterium-mediated transient overexpression technique was used to overexpress Chl H and POLGAMMA2 genes in Forsythia.Although there was no color change in the leaves of Forsythia,the content of chlorophyll increased significantly.It speculated that Chl H gene could regulate the chlorophyll content in the leaves of Forsythia by controlling the pathway of chlorophyll synthesis,and POLGAMMA2 gene could regulate the chlorophyll content by regulating the chloroplast thylakoid structure.(4)Using the second-generation transcriptome sequencing technology to analyze the function of Chl H and POLGAMMA2 gene.The yellow Forsythia’s leaves whose Chl H and POLGAMMA2 gene were silenced,were used for experiment,and the green leaves of the same plant were used as control.It confirmed that the Chl H gene inhibited the leaf chlorophyll synthesis pathway,thereby reducing the leaf chlorophyll content,changing leaf color and photosynthetic efficiency.POLGAMMA2 gene inhibited the formation of chloroplast thylakoid membrane structure,providing Forsythia chlorophyll with attaching environment.And then it significantly inhibited the metabolic process of the plant photosynthetic II system and the synthesis of chlorophyll,which reduced the photosynthetic efficiency of the leaves of Forsythia and the leaves of Forsythia became yellow.In all,it was speculated that Chl H and POLGAMMA2 genes could regulate the leaf color of Forsythia.Chl H gene affected leaf color of Forsythia by controlling leaf chlorophyll synthesis pathways.POLGAMMA2 gene affected leaf color of Forsythia by controlling the formation of chloroplast.This experiment provided the theoretical explanation for exploring the coloring mechanism of Forsythia leaves.