AP2/ERF Transcription Factors Integrate Age and Wound Signals for Root Regeneration.

Age and wounding are two major determinants for regeneration. In plants, the root regeneration is triggered by wound-induced auxin biosynthesis. As plants age, the root regenerative capacity gradually decreases. How wounding leads to the auxin burst and how age and wound signals collaboratively regulate root regenerative capacity are poorly understood. Here, we show that the increased levels of three closely-related miR156-targeted Arabidopsis (Arabidopsis thaliana) SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors, SPL2, SPL10, and SPL11, suppress root regeneration with age by inhibiting wound-induced auxin biosynthesis. Mechanistically, we find that a subset of APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) transcription factors including ABSCISIC ACID REPRESSOR1 and ERF109 is rapidly induced by wounding and serves as a proxy for wound signal to induce auxin biosynthesis. In older plants, SPL2/10/11 directly bind to the promoters of AP2/ERFs and attenuates their induction, thereby dampening auxin accumulation at the wound. Our results thus identify AP2/ERFs as a hub for integration of age and wound signal for root regeneration.

The role of miR156 in rejuvenation in Arabidopsis thaliana.

Rejuvenation refers to the process enabling plants to regain physiological and molecular characteristics lost after entering the adult phase. The underlying molecular mechanism is poorly understood. Previous studies have revealed that microRNA156 (miR156) is highly accumulated at juvenile stage and maintains juvenile traits by repressing a group of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors. Here, we found that induction of miR156 expression in adult leaves can only restore some aspects of juvenile traits, such as loss of epidermal leaf hairs on the lower side of leaves and absence of serration at the leaf edges, but is incapable of delaying flowering and promoting adventitious root production.

Mesenchymal hamartoma of liver: magnetic resonance imaging and histopathologic correlation.

AIM: To describe the imaging features of hepatic mesenchymal hamartoma with emphasis on magnetic resonance imaging (MRI) compared to histopathologic results. METHODS: Spin-echo sequence(SE),fast spin-echo sequence(FSE) were performed in 12 children (7 males,5 females) with mesenchymal hamartoma of the liver (MHL), aged 1.2 months to 12 years;( mean age, 6.3 years) axial, saggital, coronary plain imaging with an Elscint 2.0T MR equipment. Their main symptoms were abdominal mass (5 cases), enlarged liver (8 cases), abdominal pain (1 case) and anemia (2 cases), and negative alphafetoprotein. Dynamic enhancement examination was added in 2 cases. RESULTS: Six cases had single mass type of MHL, in which 3 cases had solid masses showing slight low-signal-intensity in T1WI, and irregular high-signal-intensity in T2WI, 1 case had a cystic-solid mixed mass showing several border-clear cysts in a solid mass, 2 cases had cystic masses with multi-septa. Five cases had diffuse and multifocal lesions type of MHL with its signal intensity being similar to that of the solid mass. One case had a combined diffuse and single cystic mass. In the early dynamic enhancement examination, the lesions were slightly circum-enhanced , and the center was enhanced in the later scan images. Inner hepatic vessels were compressed in 5 cases, vena cava and abdominal aortae were compressed in 3 cases. Pathological findings included fiber hyperplasia, hyaline degeneration, biliary duct hyperplasia, lobule-like array. CONCLUSION: MR imaging is a better way to differentiate and diagnose MHL. MHL may be recognized by its characteristic occurrence in infancy and MR imaging features.