Abstract
We previously found that B and AGL6 proteins form L (OAP3-2/OAGL6-2/OPI) and SP (OAP3-1/OAGL6-1/OPI) complexes to determine lip/sepal/petal identities in orchids. Here, we show that the functional L’ (OAP3-1/OAGL6-2/OPI) and SP’ (OAP3-2/OAGL6-1/OPI) complexes likely exist and AP3/PI/AGL6 genes have acquired additional functions during evolution. We demonstrate that the presumed L’ complex changes the structure of the lower lateral sepals and helps the lips fit properly in the center of the flower. In addition, we find that OAP3-1/OAGL6-1/OPI in SP along with presumed SP’ complexes regulate anthocyanin accumulation and pigmentation, whereas presumed L’ along with OAP3-2/OAGL6-2/OPI in L complexes promotes red spot formation in the perianth. Furthermore, the B functional proteins OAP3-1/OPI and OAGL6-1 in the SP complex could function separately to suppress sepal/petal senescence and promote pedicel abscission, respectively. These findings expand the current knowledge behind the multifunctional evolution of the B and AGL6 genes in plants.
Highlights
We previously found that B and AGL6 proteins form L (OAP3-2/OAGL6-2/OPI) and SP (OAP3-1/OAGL6-1/OPI) complexes to determine lip/sepal/petal identities in orchids
OAGL6-2 is mainly expressed in the lower part of the lateral sepals in different Phalaenopsis varieties (Fig. 1d) (Supplementary Fig. 1a–o) and in various species of orchids (Supplementary Fig. 2a–r), whereas the SP complexassociated gene OAGL6-1 is expressed evenly in all parts of the lateral sepals (Fig. 1e, f) (Supplementary Fig. 1p–t)
This study further showed the involvement of the proposed L′ complex
Summary
We previously found that B and AGL6 proteins form L (OAP3-2/OAGL6-2/OPI) and SP (OAP3-1/OAGL6-1/OPI) complexes to determine lip/sepal/petal identities in orchids. The B functional proteins OAP3-1/OPI and OAGL6-1 in the SP complex could function separately to suppress sepal/petal senescence and promote pedicel abscission, respectively. These findings expand the current knowledge behind the multifunctional evolution of the B and AGL6 genes in plants. L and SP complex genes are continuously expressed throughout flower development[6], suggesting that OAP3, OPI and OAGL6 may have additional functions during organ morphogenesis. To uncover these questions, we used virus-induced gene silencing (VIGS)-based gene knockdown to comprehensively functionally characterize the genes from the L and SP complexes and their target networks in Phalaenopsis orchids. SP complex proteins OAGL6-1 is found to be able to promote pedicel abscission whereas OAP3-1/OPI could function to suppress sepal/petal senescence
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