关键词: 龙眼, 褪黑素, SNAT, ASMT, COMT, 全基因组鉴定, 表达分析

Abstract:

In this study,on the basis of the third-generation longan（Dimocarpus longan Lour.）genome and transcriptome database,the possible rate-limiting genes of melatonin synthesis：SNAT（serotonin N-acetyltransferase）,ASMT（N-acetylserotonin methyltransferase）and COMT（caffeic acid O-methyltransferase）family genes were identified and analyzed. The effect of different exogenous phytohormones on the melatonin content was detected,and,the expression patterns of SNAT,ASMT,and COMT genes in respond to exogenous phytohormone treaments and during early somatic embryogenesis（SE）in longan were determined by quantitative real time polymerase chain reaction（qRT-PCR）. The results showed that the longan SNAT（DlSNAT）,ASMT（DlASMT）,and COMT（DlCOMT）family genes have two,18,and seven members,respectively;the protein domains and motifs in each same gene family are conserved,and DlASMTs and DlCOMTs are highly similar;phylogenetic analysis showed that the SNAT family of Dimocarpus longan,Arabidopsis thaliana,Oryza sativa,Triticum aestivum,Solanum lycopersicum,Capsicum annuum,and Selaginella tamariscina could be divided into three subgroups,while the ASMT and COMT families were highly homology and were divided into three subgroups;the cis-acting elements analysis revealed that a large number of auxin-,gibberellin-,methyl jasmonate-,salicylic acid-,and abscisic acid-related elements existed in the promoters of DlSNAT,DlASMT and DlCOMT family members;qRT-PCR analysis showed that most of DlASMTs and DlCOMTs were highly expressed in the incomplete embryonic compact structure and globular embryo stages of somatic embryo（SE）,while DlSNAT1 and DlSNAT2 were highly expressed during early SE in longan;the content of endogenous melatonin was significantly reduced under exogenous 0.1 mmol · L^-1 of indole-3-acetic acid（IAA）treatment,whereas significantly increased under exogenous gibberellin A3（GA₃）,methyl jasmonate（MeJA）,salicylicacid（SA）and abscisic acid（ABA）treatments;at the same time,the expression changes of DlSNATs consist with the change trends of endogenous melatonin content. The results indicated that DlSNATs,DlASMTs and DlCOMTs may involved in the synthesis of endogenous melatonin thereby regulate the process of early SE in longan.

Key words: longan, melatonin, SNAT, ASMT, COMT, whole-genome identification, expression analysis