Identification and evolution of floral organ identity genehomologues in Buxus microphylla ssp. sinica (Buxaceae)

• Main Authors: Nai-Luen Huang, 黃乃倫
• Other Authors: 胡哲明
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/61092883353996357306

碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 94 === Floral organ determination is best explained by the ABCDE model postulated by genetic studies of Arabidopsis thaliana. Sepals are determined by A and E class genes; petals are determined by A, B, and E; stamens by B, C, and E; and carpels by C and E class genes. A, B, C, and E class gene lineages are known having duplicated several times during the evolution of angiosperms. One of the noted major duplication events occurred in the origin of the early angiosperms, leading to the formation of subgroups of B/C/D/E class. Another one occurred near the basal eudicots and gave rise to further subgroups in A/B/C/D/E class genes among core eudicots. The phylogenetic position of the family Buxaceae is located right where the second major duplication of ABCDE genes might have occurred, which is supported by multiple gene (nuclear 18S rDNA, chloroplast rbcL and atpB) phylogenetic analyses. Therefore, the identification and characterization of floral organ identity genes in Buxaceae is critical in elucidating the gene evolution related to floral organ formation. Floral organ identity gene homologues of Buxus microphylla ssp. sinica were screened, and nine gene homologues of B. microphylla ssp. sinica were successfully identified in this study. Two of them are A class gene homologues, four B class, two C class, and one E class. Expression patterns based on RT-PCR of floral organ identity genes of Buxus do not match with current ABCDE model. There is no expression of all identified genes in leaves, and all genes are expressed in all floral parts except BumPI2. BumPI2 does not express in pistillodes, and only weakly expresses in stamens. Whether or not the discrepancy is due to a deviation from the standard floral model awaits further examinations. According to the phylogenetic analyses, the homologous genes of Buxus belong to their expected clades, showing a position near the base of core eudicots. Genes of Buxus are always sister to genes of Pachysandra or Trochodendron,and this clade is close to core eudicots in all analysis. BumAP3 genes are the only exception that sometimes grouped with Pachysandra genes as sister group to euAP3 clade. Moreover, frameshift modulation of BumAP3-1/2/3 genes indicates their high frameshift potential and frameshift mutation might be the key mechanism occurred after duplication event and led to diversification of core eudicots.