Evolução e desenvolvimento de gavinhas em Bignonieae (Bignoniaceae) / Evolution and development of tendrils in Bignonieae (Bignoniaceae)

Mariane Silveira de Sousa Baena

Angiosperm leaves have undergone major functional and structural modifications over time, and currently exist in a wide diversity of forms, sizes, and arrangements. For example, in the tribe Bignonieae (Bignoniaceae), leaves are generally 2-3-foliolated, and the terminal leaflet is often modified into tendrils.These tendrils present varied morphologies (simple, bifid, trifid or multifid) and are thought to have been involved in the diversification of Bignonieae. Despite the importance of tendrils for climbing plants, little is still known about the biology of tendrils in the angiosperms. To date, no data is available on the genes that control tendrilled-leaf development in species other than pea (Pisum sativum). Even though KNOX1 genes control leaf development in the majority of compound-leaved angiosperms, in pea, KNOX1 is completely excluded from the leaf primordium and its development is regulated by LEAFY/FLORICAULA (LFY/FLO). This observation suggests that the development of other tendrilled-leaves might also be exclusively regulated by LFY/FLO as well. This study investigated the evolution and development of tendril types in Bignonieae in order to further understand how changes in leaf morphogenesis led to current patterns of variation in tendril morphology. We further analyzed the expression patterns of SHOOTMERISTEMLESS (STM, KNOX1 gene), PHANTASTICA (PHAN) and LFY/FLO during leaf development in three representatives of Bignonieae with different tendril types in order to better understand the structure, origin and genetic basis of leaf tendrils in this plant clade. Our results demonstrate that leaves in Bignonieae develop acropetally, as well as indicates that trifid tendrils are ancestral in the tribe, with the evolution of other tendril types involving heterochonic shifts in the leaf basic developmental pathway. Furthermore, transcripts of STM were detected in developing leaves, revealing that tendrilled leaves of Bignonieae develop differently from those of pea. The anatomical analysis revealed that tendrils are bilaterally symmetrical and present some characteristics that are similar to leaflets, further corroborating earlier suggestions that tendrils indeed represent modified leaflets. This observation was further reinforced by the expression pattern of PHAN (an adaxial identity gene), as PHAN transcripts were confined to the adaxial domain of the tendril primordia in branched-tendrilled species, in a pattern very similar to that observed in leaflet primordia. In B. callistegioides, a simple-tendrilled species, PHAN was expressed throughout the entire tendril, indicating a certain degree of disruption in the establishment of the adaxial domain. The differences encountered in the expression pattern of PHAN amongst species with different tendril types indicate a possible correlation of the expression of PHAN with tendril branching. Furthermore, it suggests an important role for PHAN in the establishment of tendril polarity and in the rise of the various tendril types encountered in Bignonieae. In addition, the pattern of expression of LFY/FLO in developing leaves has led us to infer that LFY/FLO may present an important role for the separation of new organs from meristematic zones.

Evolução e desenvolvimento de gavinhas em Bignonieae (Bignoniaceae) / Evolution and development of tendrils in Bignonieae (Bignoniaceae)

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