Zamira Abraham

Comparative phylogenetic analysis of cystatin gene families from arabidopsis, rice and barley

The plant cystatins or phytocystatins comprise a family of specific inhibitors of cysteine proteinases. Such inhibitors are thought to be involved in the regulation of several endogenous processes and in defence against pests and pathogens. Extensive searches in the complete rice and Arabidopsis genomes and in barley EST collections have allowed us to predict the presence of twelve different cystatin genes in rice, seven in Arabidopsis, and at least seven in barley. Structural comparisons based on alignments of all the protein sequences using the CLUSTALW program and searches for conserved motifs using the MEME program have revealed broad conservation of the main motifs characteristic of the plant cystatins. Phylogenetic analyses based on their deduced amino acid sequences have allowed us to identify groups of orthologous cystatins, and to establish homologies and define examples of gene duplications mainly among the rice and barley cystatin genes. Moreover, the absence of a counterpart between the two monocots, as well as strong variations in the motifs that interact with the cysteine proteinases, may be related to a species-specific evolutionary process. This cystatin classification should facilitate the assignment of proteinase specificities and functions to other cystatins as new information is obtained.

SKP2A protein, an F-box that regulates cell division, is degraded via the ubiquitin pathway

The ubiquitin pathway is emerging as a powerful system that controls the stability of key regulatory proteins. In plants, this pathway plays an important role in controlling several developmental processes, responses to environmental changes and also cell division. Arabidopsis SKP2A is an F-box protein that regulates the stability of the E2FC-DPB transcription factor, a repressor of cell proliferation. Although the function of SKP2A is to recruit targets for degradation, we have shown that SKP2A is also degraded through the Ub/26S pathway and, interestingly, auxin stimulates such degradation. Overexpression of SKP2A positively regulates cell division, increasing the number of cells in G2/M, reducing the level of ploidy and developing higher number of lateral root primordia. In addition, we showed in this report that overexpression of SKP2A increased the survival of Arabidopsis plants when they grown on a medium with high levels of sucrose, likely by maintaining cell division active. Thus, it is likely that SKP2A connects cell division with stress responses. Addendum to: Jurado S, Díaz-Triviño S, Abraham Z, Manzano C, Gutierrez C, Del Pozo C. SKP2A, an F-box protein that regulates cell division, is degraded via the ubiquitin pathway. Plant J 2008; 53:828-41.

Ectopic Expression of E2FB , a Cell Cycle Transcription Factor, Accelerates Flowering and Increases Fruit Yield in Tomato

Cell division and plant development are two interconnected and dependent processes. Nowadays, the sequencing of plant genomes has allowed the identification of the majority of cell cycle regulators. However, the function of many of these cell cycle genes remains unclear. At present, the majority of cell cycle studies have been focused on the model plant Arabidopsis thaliana. In this model plant, the cell cycle transcription factor E2FB acts as positive regulator of cell proliferation. In this work we analyzed the effect of expressing E2FB in tomato. E2FB-expressing plants show reduced levels of cell cycle genes in mature leaves and grow and develop faster than wild type (wt). E2FBOE plants flower significantly earlier than wt and produce more and bigger fruits, with the total fruit yield significantly higher in E2FBOE than in wt plants. Taken together, our data indicate that the rate of cell proliferation and differentiation is important for tomato development and that cell cycle genes are good candidates to manipulate to improve crop productivity.