Study On The Effects Of Secondary Wall Lignin Metabolism In The Juice Sacs Of 'guanxi' Pomelo By ABA And ETH

In this experiment,The physiological indexes,quality,lignin content,granulation rate,endogenous ABA and ETH content were determined,and lignin was stained and observated in the juice sacs of four different periods by injecting the exogenous ABA and ETH into the fruits of`guanxi`pomelo(Citrus grandis).The transcriptomes of four different periods were analyzed in control group,the differential genes were screened,and were analyzed by fluorescence quantitative PCR.The main results are as follows:1.During the ripening stage of the fruits,the cell wall of juice sacs was hydrolyzed,lignin staining was light,and TSS was high.At this time,the juice sacs are juicy,moderately sweet and sour,and the juice sacs have no granulation or no obvious granulation,which was the best time to eat.ABA and ETH treatment accelerated fruit ripening,and improved significantly the granulation rate of the juice sacs,fruit weight and lignin content in November,with deeper lignin staining,lower TSS and fruit shape index.There was a positive correlation between lignin content and ABA content,and a greater correlation between endogenesis ABA and ETH content.Thus,ABA and ETH might be involved in the synthesis of the lignin in the secondary wall of the granulated juice sacs.2.40 differentially expressed genes,involving lignin synthesis,ABA synthesis,ABA signal transduction,ETH synthesis and ETH signal transduction,were screened from 4 transcriptomes in the control group,and fluorescence quantitative PCR verification was performed.Twenty-two q RT-PCR expressions were found to be consistent with transcriptome sequencing,including 12 lignin synthesis genes(Cr PAL1,Cr PAL3,Cr C4H1,Cr C4H2,Cr4 CL,Cr HCT1,Cr CCR3,Cr CAD3,Cr POD2,Cr POD7 and Cr LAC1 and Cr LAC2),2 ABA synthesis pathway genes(Cr NCED2,Cr SDR1),4 ABA signal transduction pathway genes(Cr PYR/PYL-2,Cr PP2C1,Cr Sn RK2-1,Cr Sn RK2-2),2 ethylene synthesis genes(Cr ACS,Cr ACO1)and 4 ETH signal transduction pathway genes(Cr SIMKK1,Cr SIMKK2,Cr EIN3 and Cr ERF1/2-1).3.After ABA and ETH injection,the expression levels of 10 lignin synthesis genes(Cr PAL3,Cr C4 H,Cr HCT1,Cr CCR3,Cr CAD3,Cr POD)and 2 laccase genes(Cr LAC)in the juice sacs were increased significantly in October and November compared with the control group.These results showed that ABA and ETH could promote the anabolism of the lignin and participate in the thickening of the secondary wall of the juice sacs.ABA and ETH promoted significantly the expression of ABA synthetic genes Cr NCED2,Cr SDR1,ETH synthetic genes Cr ACS and Cr ACO1,thus improving the content of ABA and ETH and promoting the ripening of the fruits.ABA and ETH stimulated significantly ABA signaltransduction pathways genes Cr PYR/ PYl-2 and CRSNRK2-1,ETH signal transduction pathways genes Cr SIMKK1,Cr SIMKK2,Cr EIN3 and Cr ERF1/2-1.These results indicated that ABA and ETH might stimulate the expression of downstream signaling pathway genes by increasing the content of ABA and ETH,so as to promote the senescence and the juice sacs granulation in the pomelo fruits.