Interactions among proteins of floral MADS‐box genes in Nuphar pumila (Nymphaeaceae) and the most recent common ancestor of extant angiosperms help understand the underlying mechanisms of the origin of the flower

Abstract

Interactions among proteins of floral MADS-box genes in Nuphar pumila (Nymphaeaceae) and the most recent common ancestor of extant angiosperms help understand the underlying mechanisms of the origin of the flower Abstract Floral organ identity genes, most of which are MADS-box genes, play key roles in flower development and floral organ identity determination. To specify the identities of different floral organ types, proteins of the floral MADS-box genes need to form dimers and higher-level complexes before they bind to the control regions of downstream genes and regulate their expression. Previous studies have shown that understanding the evolution of the interactions among proteins of the floral MADS-box genes may be an excellent step towards uncovering the underlying mechanisms of the origin of the flower. Yet, due to the lack of such information in early-branching angiosperm lineages, it has been difficult to determine the evolutionary changes of the protein-protein interactions (PPIs) before and after the origin of the flower. In this study, we first isolated counterparts of the floral MADS-box genes from Nuphar pumila (Timm) D.C., a representative of the basalmost angiosperms Nymphaeales, and investigated the interactions among their proteins by carrying out yeast two-hybrid assays. We then estimated the PPIs in the most recent common ancestor of extant angiosperms by using two different methods: ancestral character state reconstruction and ancestral sequence reconstruction followed by yeast two-hybrid assay. Based on these results, we examined the evolutionary transitions of the PPIs before and after the occurrence of extant angiosperms, and discussed their contributions to the origin of the flower. We found that duplication and diversification of floral MADS-box genes, as well as non-random losses of some once-existed PPIs, have been the driving force of the origin of the flower.

Flower Development and Perianth Identity Candidate Genes in the Basal Angiosperm Aristolochia fimbriata (Piperales: Aristolochiaceae)

“…These studies raise the question regarding the genetic complement present in basal angiosperms, and in particular in Piperales with respect to the earliest diverging angiosperms on one side and the specious monocot and eudicot clades, on the other. Our results show that A. fimbriata has a similar floral genetic toolkit to that found in the earliest diverging ANA members, Amborella trichopoda (Amborellaceae) and Nuphar pumila (Nymphaeaceae; Amborella Genome Project, 2013 ; Li et al, 2015 ). The A. fimbriata flower and fruit mixed transcriptome allowed us to find expression of a single copy of each A, C, D-class, and AGL6 MADS-box clade, and two paralogs for the B and the E-class genes, which are known to have duplicated prior to the diversification of angiosperms likely in the ε WGD event ( Figure 5 ; Kramer et al, 1998 ; Becker and Theissen, 2003 ; Zahn et al, 2005 ).…”

Prevalent Exon-Intron Structural Changes in the APETALA1/FRUITFULL, SEPALLATA, AGAMOUS-LIKE6, and FLOWERING LOCUS C MADS-Box Gene Subfamilies Provide New Insights into Their Evolution

“…Biochemical data revealed that the SEP-like proteins are able to form quaternary complexes with other floral MADS-box proteins in many species, such as Arabidopsis , petunia, Gerbera hybrida, Vitis vinifera , and rice (Honma and Goto, 2001 ; Ferrario et al, 2003 ; Ruokolainen et al, 2010 ; Seok et al, 2010 ; Smaczniak et al, 2012 ; Mellway and Lund, 2013 ). Recently, we reported that heterodimers between the SEP-like proteins and other floral MADS-box proteins can be formed in early diverging angiosperms, such as Amborella and Nuphar pumila ( Amborella Genome Project, 2013 ; Li et al, 2015 ). Moreover, by conducting yeast two-hybrid assays with resurrected proteins of the MRCA of extant angiosperms, we found that the ancestral SEP-like proteins have broad interactions with other ancestral floral MADS-box proteins (Li et al, 2015 ).…”

“…Recently, we reported that heterodimers between the SEP-like proteins and other floral MADS-box proteins can be formed in early diverging angiosperms, such as Amborella and Nuphar pumila ( Amborella Genome Project, 2013 ; Li et al, 2015 ). Moreover, by conducting yeast two-hybrid assays with resurrected proteins of the MRCA of extant angiosperms, we found that the ancestral SEP-like proteins have broad interactions with other ancestral floral MADS-box proteins (Li et al, 2015 ). Therefore, it is highly likely that the SEP -like gene in the MRCA of extant angiosperms has obtained the function of determining floral organ identities and the ability to mediate the formation of floral quartets, which has been retained during the evolution due to their stable gene structures and conserved sequence features.…”

How did the flower originate?

“…他 们 认 为 : 在 花 的 发 育 过 程 中 , LFY表达量的持续升高会导致生殖轴基部和顶部B类 和C类基因表达量的改变以及四聚体组成的差异, 结 果促成了两性花的形成. 随后, Theißen和Melzer [4] [54,69,70] . [71] .…”

“…方式上发生了明显改变 [70,78,79] [47,80~85] , 并且发 现有些基因可能与花起源过程中一些关键性状的出 现有关. 例如, INO (INNER NO OUTER)基因被认为 可能与外珠被的起源有关 [86] , 而CRC(CRABS CLAW)、 HEC(HECATE)和NGA (NGATHA)基因在被子植物最 近 共 同 祖 先 中 的 起 源 以 及 LUG (LEUNIG) 、SEU (SEUSS) 和 SHI/STY(SHORT INTERNODE/STYLISH) 基 因的重复和分化可能与心皮发育调控网络的建立和 心皮的起源有关 [27,45,46] .…”