The role of gibberellin metabolic genes in anisocotyly development of Streptocarpus rexii (Gesneriaceae)
Date Issued
2012
Date
2012
Author(s)
Ho, Meng-Jung
Abstract
Anisocotyly is an unorthodox phenomenon among angiosperms, found only in the family members of Gesneriaceae. The rosulate species Streptocarpus rexii exhibits an anisocotylous growth pattern as one of its cotyledons (macrocotyledon) grows continuously via sustained basal meristem (BM) activity at the proximal end. Previous findings suggest that exogenous gibberellin (GA3) can inhibit anisocotyly via suppression of the formation of the BM, causing two equal-sized, small microcotyledons. This study is therefore aimed to shed light on the role of gibberellin (GA) in anisocotyly by revealing the expression pattern of GA catabolism and biosynthesis genes, SrGA2ox and SrGA20ox, to determine how they regulate the unusual basal meristem activity that gives rise to anisocotyly in S. rexii. RT-PCR and RNA in situ hybridization demonstrated that in the macrocotyledon, SrGA2ox shows restricted expression in the basal meristem and also in a shoot apical meristem (SAM) equivalent groove meristem (GM), where further phyllomorph and inflorescence are produced. On the contrary, SrGA20ox transcripts, distributed in the microcotyledon and the distal end of the macrocotyledon, never distributed in the meristem area. These results show agreement with that of model plants, which also suggest that a low concentration of GA is necessary for maintaining meristem activity. Moreover, this mutually exclusive expression pattern between SrGA2ox and SrGA20ox was established since the embryo stage. SrGA2ox was expressed on the adaxial side of both cotyledons, whereas SrGA20ox was distributed in the shoot meristem (SM) and abaxial side of the cotyledons during the embryo stage. The expression of SrGA20ox in the SM may explain the lack of normal shoot initiation in S. rexii seedlings. Because it is also known that exogenous cytokinin (CK) can induce both cotyledons into macrocotyledons, further investigation on the expression profiles of CK genes and their interaction with GA genes is important to fully uncover the developmental mechanism of anisocotyly.
Subjects
Anisocotyly
Type
thesis
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