Agrobacterium tumefaciens is a gram-negative soil bacterium that induces plant tumors by transferring a segment of DNA, called T-DNA, into plant cells. Under laboratory conditions, Agrobacterium... Show moreAgrobacterium tumefaciens is a gram-negative soil bacterium that induces plant tumors by transferring a segment of DNA, called T-DNA, into plant cells. Under laboratory conditions, Agrobacterium can also transform many different non-plant organisms such as the yeast Saccharomyces cerevisiae. During this process, a number of virulence proteins, including VirF and VirE3, are translocated into the host cell. VirF contains an F-box domain and, according to current theory, in plants and in yeast may induce degradation of the virulence protein VirE2 and the transcription factor VIP1, required for the integration of the T-DNA into host chromosomal DNA. VirE3 functions as a potential plant transcriptional activator. In our study, we expressed the Agrobacterium virulence proteins VirF and VirE3 in Saccharomyces cerevisiae and Arabidopsis thaliana and studied the effect of virF and virE3 expression on the genome-wide transcription in S. cerevisiae and A.thaliana using DNA microarrays and RNA-sequencing. Show less
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... Show moreWhat 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. Show less
