Functional Identification Of AGL6 Clade Genes During Floral Organ Development

The study of flower development is the hotspot of plant developmental biology core while ABCDE model illustrated the molecular mechanisms of floral development as general principles. The MADS-box genes involved in ABCDE model are almost restricted to the MIKC subfamily. AP1/AGL9 group in MIKC subfamily was split into AP1, AGL6/AGL13, SEP clades. AP1 clade and SEP clade are factors of ABCDE model and much researches have been made on the functions and mechanisms of AP1 clade and SEP clades. Although AGL6 clade genes have been cloned from different types of plants, but their functions and mechanisms are less well characterized.In order to study the roles of AGL6 clade genes in Hyacinthus orientalis, we isolated a MADS box gene HoAGL6 grouped to Arabidopsis AGL6 clade from floral buds of Hyacinthus based on PCR strategy. Expression pattern analysis demonstrated that HoAGL6 transcript was detected in inflorescence buds, tepals, carpels and ovules, but not in stamina, leaves or scales and that suggests HoAGL6 in flower formation, and tepal and ovary development. The expression vector of HoAGL6 gene was constructed and transformed into Arabidopsis plants and Transgenic Arabidopsis plants ectopically expressing HoAGL6 exhibited novel phenotypes of significantly reduced plant size, extremely early flowering, and losing inflorescence indeterminacy. The result showed that HoAGL6 was involved in flowering time regulation. In addition, wide homeotic conversion of sepals, petals, and leaves into carpel-like or ovary structures, and disappearance or number reduction of stamens in 35S::HoAGL6 Arabidopsis plants were also observed. This result indicated that HoAGL6 was involved in floral formation and floral organ initiation in transgenic plants. RT-PCR analysis indicated that the expressions of flowering time gene SOC1 and flower meristem identity gene LFY were significantly up-regulated in 35S::HoAGL6 transgenic Arabidopsis plants, and the expression levels of floral organ identity genes AG and SEP1 in leaves were also elevated. These results indicated that HoAGL6 was involved in the regulation of flower transition and flower organ formation.Based on the mechanistic analysis of hyacinth HoAGL6 in floral organ determination, We can infer that AGL6-like genes as a new class of factors are involved in the mechanism of floral organ development revealed in the ABCDE model, serving as an activator and partner. We propose that the dynamic behavior of the four groups of MADS-box proteins is perfectly responsible for morphogenesis of the four floral organ types. The first sepal whorl is sufficiently specified by concomitance of AP1, SEP, SVP, AGL6. The petal whorl could be fully specified by concomitance of AP1, AP3/PI, SEP and AGL6. The third stamen whorl would be determined by a group of polymers basically composed of AP3/PI, SEP, AG and AGL6. The fourth whorl could be controlled by a tetramer array of STK/SHP, AG, SEP and AGL6.In order to study functions of AGL6 clade genes from model plants, we isolated AGL6 gene from floral buds of Arabidopsis based on PCR strategy. The expression vector of AGL6 gene was constructed and transformed into Arabidopsis plants. We are conducting the functional analysis at present.