The Arabidopsis RTH plays an important role in regulation of iron (Fe) absorption and transport

KEY MESSAGE

RTH may activate Fe assimilation related genes to promote Fe absorption, transport and accumulation in Arabidopsis. Iron (Fe) is an important nutrient element. The Fe absorption and transport in plants are well investigated over the past decade. Our previous work indicated that RTE1-HOMOLOG (RTH), the homologous gene of reversion-to-ethylene sensitivity 1 (RTE1), plays a role in ethylene signaling pathway. However, its function in Fe absorption and transport is largely unknown. In the present study, we found that RTH was expressed in absorptive tissue and conducting tissue, including root hairs, root vascular bundle, and leaf veins. Under high Fe concentration, the seedling growth of rth-1 mutant was better, while the RTH overexpression lines were retarded compared to the wild type (Col-0). When treated with EDTA-Fe3+ (400 μM), the chlorophyll content and ion leakage rate were higher and lower in rth-1 than those of Col-0, respectively. By contrast, the chlorophyll contents and ion leakage rates of RTH overexpression lines were decreased and hastened compared with Col-0, respectively. Fe measurement indicated that the Fe contents of rth-1 were lower than those of Col-0, whereas those of RTH overexpression lines were comparably higher. Gene expression analysis revealed that Fe absorption and transport genes AHA2, IRT1, FIT, FPN1, and YSL1 decreased in rth-1 but increased in RTH overexpression lines compared with Col-0. Additionally, Y2H (yeast two-hybrid) and BiFC (bimolecular fluorescence complementation) assays showed that RTH can physically interact with hemoglobin 1 (HB1) and HB2. All these findings suggest that RTH may play an important role in regulation of Fe absorption, transport, and accumulation in Arabidopsis.

Resistance to Thyroid Hormones: A Case-Series Study

The aim of the study is to describe the clinical features of two unrelated patients with resistance to thyroid hormones (RTH), the first, a total thyroidectomized patient, and the second, a pregnant woman. We report the features found in her newborn who also showed RTH. Patient 1 is a 38-year-old man with total thyroidectomy managed for excessive thyroid stimulating hormone (TSH) production, which poorly responded to the replacement therapy. He was found with a THRβ c.1378G>A p.(Glu460Lys) heterozygous mutation, which was also present in other members of his family (son, brother, and father). Interestingly, Patient 1 had hypertension, dyslipidemia, and hepatic steatosis, which have been recently suggested as RTH-related comorbidities. Patient 2 is a 32-year-old pregnant woman with multinodular goiter, and the THRβ heterozygous variant c.959G>C, that, to the best of our knowledge, has been reported in literature only once. Her newborn had tachycardia and increased thyroid hormone levels, and showed the same mutation. After delivery, high parathyroid hormone (PTH) and calcium serum levels were found in Patient 2 and the scintigraphy showed the presence of adenoma of a parathyroid gland. This case-series study provides a practical example of the management of RTH in a thyroidectomized patient, a pregnant woman, and a newborn. A novel RTH pathogenic mutation is described for the second time in literature. Furthermore, the importance of metabolic assessment in patients with RTHβ has been highlighted and the possible correlation between RTH and primary hyperparathyroidism is discussed.

A resistance to thyroid hormone syndrome mutant operates through the target gene repertoire of the wild-type thyroid hormone receptor

Thyroid hormone receptors (TRs) play crucial roles in vertebrates. Wild-type (WT) TRs function primarily as hormone-regulated transcription factors. A human endocrine disease, Resistance to Thyroid Hormone (RTH)-Syndrome, is caused by inheritance of mutant TRs impaired in the proper regulation of target gene expression. To better understand the molecular basis of RTH we compared the target genes regulated by an RTH-TRβ1 mutant (R429Q) to those regulated by WT-TRβ1. With only a few potential exceptions, the vast majority of genes we were able to identify as regulated by the WT-TRβ1, positively or negatively, were also regulated by the RTH-TRβ1 mutant. We conclude that the actions of R429Q-TRβ1 in RTH-Syndrome most likely reflect the reduced hormone affinity observed for this mutant rather than an alteration in target gene repertoire. Our results highlight the importance of target gene specificity in defining the disease phenotype and improve our understanding of how clinical treatments impact RTH-Syndrome.