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The common bottlenose dolphin (Tursiops truncatus) is a key marine mammal species in the Gulf of Mexico, playing an essential role as a top predator. This study investigates the genetic diversity and population structure of bottlenose dolphins stranded in the Mississippi Sound from 2010 to 2021. Tissue samples (muscle, liver, lung, kidney, and brain) were collected from 511 stranded dolphins, and mitochondrial DNAs (mtDNA) were extracted for analysis. A total of 417 samples were successfully amplified and sequenced using high throughput sequencing, yielding 386 complete mitogenomes. Genetic diversity metrics, such as nucleotide and haplotype diversity, were calculated, and population structure was inferred for both mitochondrial control region (mtCR) and whole mitogenome sequences. Using the whole mitogenome, the study identified four genetically distinct populations within the Mississippi Sound, demonstrating regional variation in dolphin populations. Notably, two stranded individuals likely originated from populations outside the sampled area. The use of whole mitogenomes allowed for improved resolution of genetic diversity and population differentiation compared to previous studies using partial mtDNA sequences. These findings enhance our understanding of bottlenose dolphin population structure in the region and underscore the value of stranded animals for population genetic studies. 

Abstract Background Nuclear endosperm development is a common mechanism among Angiosperms, including Arabidopsis. During nuclear development, the endosperm nuclei divide rapidly after fertilization without cytokinesis to enter the syncytial phase, which is then followed by the cellularized phase. The endosperm can be divided into three spatial domains with distinct functions: the micropylar, peripheral, and chalazal domains. Previously, we identified two putative small invertase inhibitors, InvINH1 and InvINH2, that are specifically expressed in the micropylar region of the syncytial endosperm. In addition, ectopically expressing InvINH1 in the cellularized endosperm led to a reduction in embryo growth rate. However, it is not clear what are the upstream regulators responsible for the specific expression of InvINHs in the syncytial endosperm. Results Using protoplast transient expression system, we discovered that a group of type I MADS box transcription factors can form dimers to activate InvINH1 promoter. Promoter deletion assays carried out in the protoplast system revealed the presence of an enhancer region in InvINH1 promoter, which contains several consensus cis-elements for the MADS box proteins. Using promoter deletion assay in planta , we further demonstrated that this enhancer region is required for InvINH1 expression in the syncytial endosperm. One of the MADS box genes, AGL62, is a key transcription factor required for syncytial endosperm development. Using promoter-GFP reporter assay, we demonstrated that InvINH1 and InvINH2 are not expressed in agl62 mutant seeds. Collectively, our data supports the role of AGL62 and other type I MADS box genes as the upstream activators of InvINHs expression in the syncytial endosperm. Conclusions Our findings revealed several type I MADS box genes that are responsible for activating InvINH1 in the syncytial endosperm, which in turn regulates embryo growth rate during early stage of seed development.