AUTHOR=Zhu Butuo , Li Hui , Wen Jiangqi , Mysore Kirankumar S. , Wang Xianbing , Pei Yanxi , Niu Lifang , Lin Hao 

TITLE=Functional Specialization of Duplicated AGAMOUS Homologs in Regulating Floral Organ Development of Medicago truncatula

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00854

DOI=10.3389/fpls.2018.00854

ISSN=1664-462X

ABSTRACT=<p>The C function gene <italic>AGAMOUS</italic> (<italic>AG</italic>) encodes for a MADS-box transcription factor required for floral organ identity and floral meristem (FM) determinacy in angiosperms. Unlike Arabidopsis, most legume plants possess two <italic>AG</italic> homologs arose by an ancient genome duplication event. Recently, two <italic>euAGAMOUS</italic> genes, <italic>MtAGa</italic> and <italic>MtAGb</italic>, were characterized and shown to fulfill the C function activity in the model legume <italic>Medicago truncatula</italic>. Here, we reported the isolation and characterization of a new <italic>mtaga</italic> allele by screening the <italic>Medicago Tnt1</italic> insertion mutant collection. We found that <italic>MtAGa</italic> was not only required for controlling the stamen and carpel identity but also affected pod and seed development. Genetic analysis indicated that <italic>MtAGa</italic> and <italic>MtAGb</italic> redundantly control <italic>Medicago</italic> floral organ identity, but have minimal distinct functions in regulating stamen and carpel development in a dose-dependent manner. Interestingly, the stamens and carpels are mostly converted to numerous vexillum-like petals in the double mutant of <italic>mtaga mtagb</italic>, which is distinguished from Arabidopsis <italic>ag</italic>. Further qRT-PCR analysis in different <italic>mtag</italic> mutants revealed that <italic>MtAGa</italic> and <italic>MtAGb</italic> can repress the expression of putative A and B function genes as well as <italic>MtWUS</italic>, but promote putative D function genes expression in <italic>M. truncatula</italic>. In addition, we found that the abnormal dorsal petal phenotype observed in the <italic>mtaga mtagb</italic> double mutant is associated with the upregulation of <italic>CYCLOIDEA</italic> (<italic>CYC</italic>)-like TCP genes. Taken together, our data suggest that the redundant <italic>MtAGa</italic> and <italic>MtAGb</italic> genes of <italic>M. truncatula</italic> employ a conserved mechanism of action similar to Arabidopsis in determining floral organ identity and FM determinacy but may have evolved distinct function in regulating floral symmetry by coordinating with specific floral dorsoventral identity factors.</p>