Protein ubiquitination in auxin signaling and transport

What makes plant shoots grow towards the light, and plant roots grow down into the soil? This was a question that Charles Darwin asked himself, and his experiments more than a century ago to find the answer laid the basis for the identification of the growth hormone auxin. Auxin, or indole-3-acetic acid (IAA), directs plant growth and development through its polar cell-to-cell transport-driven asymmetric distribution. Cellular IAA concentrations determine cell division, -elongation and -differentiation by facilitating the degradation of the Aux/IAA repressor proteins and thus inducing gene expression. The presumed pathway for the programmed degradation of proteins involves the attachment of a protein called ubiquitin, leading to recognition and destruction by a molecular complex called the proteasome. Here we investigated the role of protein ubiquitination and degradation in auxin action. First, we provided evidence for the longstanding paradigm that Aux/IAA proteins are ubiquitinated prior to their proteasomal degradation. At the same time we showed that ubiquitin labeling is not necessarily required for proteasomal degradation of plant proteins. Moreover, we showed that a regulator of auxin transport polarity is also involved in fine tuning auxin responses through the ubiquitin pathway. Our results place protein ubiquitination at a central position in auxin biology and thus in the movement of plants.UBL - phd migration 201

Effects of light intensity on root development in a D-Root growth system

Plant development is highly affected by light quality, direction, and intensity. Under natural growth conditions, shoots are directly exposed to light whereas roots develop underground shielded from direct illumination. The photomorphogenic development strongly represses shoot elongation whereas promotes root growth. Over the years, several studies helped the elucidation of signaling elements that coordinate light perception and underlying developmental outputs. Light exposure of the shoots has diverse effects on main root growth and lateral root (LR) formation. In this study, we evaluated the phenotypic root responses of wild-type Arabidopsis plants, as well as several mutants, grown in a D-Root system. We observed that sucrose and light act synergistically to promote root growth and that sucrose alone cannot overcome the light requirement for root growth. We also have shown that roots respond to the light intensity applied to the shoot by changes in primary and LR development. Loss-of-function mutants for several root light-response genes display varying phenotypes according to the light intensity to which shoots are exposed. Low light intensity strongly impaired LR development for most genotypes. Only vid-27 and pils4 mutants showed higher LR density at 40 mu mol m(-2) s(-1) than at 80 mu mol m(-2) s(-1) whereas yuc3 and shy2-2 presented no LR development in any light condition, reinforcing the importance of auxin signaling in light-dependent root development. Our results support the use of D-Root systems to avoid the effects of direct root illumination that might lead to artifacts and unnatural phenotypic outputs

Phytotoxicity of the extracts of Lonchocarpus muehlbergianus Hassl. (Fabaceae) leaflets and galls on seed germination and early development of lettuce

Galls induced by Euphalerus ostreoides (Hemiptera: Psyllidae) cause structural and chemical alterations on Lonchocarpus muehlbergianus leaflets. Healthy and galled leaflet tissues of this plant species are rich in secondary metabolites with potential allelopathic effects. This research compares the allelopathic effects of the aqueous extracts of L. muehlbergianus leaflets and galls on seeds and seedlings of Lactuta sativa, and evaluates the chemical impact produced by a gall-inducing insect on the other trophic levels associated with it. The extracts were obtained through static maceration in distilled water (5% p/v). The treatments consisted of aqueous crude extracts and those previously filtered in polyvinylpirrolidone (PVP). After seven days, seedling height was measured, and the radicles were fixed in FAA50 for anatomical analyses. Healthy leaflet and gall aqueous extracts, and those filtered in PVP, significantly inhibited seed germination, with no significant differences between the two groups. Treatments with aqueous extracts reduced seed germination speed and vegetative axis length. Plant tissue alterations confirm the phytotoxicity of allelochemical substances present in the extracts. The differences among the treatments indicated that gall formation altered L. muehlbergianus leaflet metabolism, and this could influence the other trophic levels associated with this gall inducing-host plant system