Structure-Based Modulation of the Ligand Sensitivity of a Tomato Dimeric Abscisic Acid Receptor Through a Glu to Asp Mutation in the Latch Loop.

The binding of the plant phytohormone Abscisic acid (ABA) to the family of ABA receptors (PYR/PYL/RCAR) triggers plant responses to abiotic stress. Thus, the implementation of genetic or chemical strategies to modulate PYR/PYL activity might be biotechnologically relevant. We have employed the available structural information on the PYR/PYL receptors to design SlPYL1, a tomato receptor, harboring a single point mutation that displays enhanced ABA dependent and independent activity. Interestingly, crystallographic studies show that this mutation is not directly involved in ABA recognition or in the downstream phosphatase (PP2C) inhibitory interaction, rather, molecular dynamic based ensemble refinement restrained by crystallographic data indicates that it enhances the conformational variability required for receptor activation and it is involved in the stabilization of an active form of the receptor. Moreover, structural studies on this receptor have led to the identification of niacin as an ABA antagonist molecule in vivo. We have found that niacin blocks the ABA binding site by mimicking ABA receptor interactions, and the niacin interaction inhibits the biochemical activity of the receptor.

RGL2 controls flower development, ovule number and fertility in Arabidopsis.

DELLA proteins are a group of plant specific GRAS proteins of transcriptional regulators that have a key role in gibberellin (GA) signaling. In Arabidopsis, the DELLA family is formed by five members. The complexity of this gene family raises the question on whether single DELLA proteins have specific or overlapping functions in the control of several GA-dependent developmental processes. To better understand the roles played by RGL2, one of the DELLA proteins in Arabidopsis, two transgenic lines that express fusion proteins of Venus-RGL2 and a dominant version of RGL2, YPet-rgl2Δ17, were generated by recombineering strategy using a genomic clone that contained the RGL2 gene. The dominant YPet-rgl2Δ17 protein is not degraded by GAs, and therefore it blocks the RGL2-dependent GA signaling and hence RGL2-dependent development. The RGL2 role in seed germination was further confirmed using these genetic tools, while new functions of RGL2 in plant development were uncovered. RGL2 has a clear function in the regulation of flower development, particularly stamen growth and anther dehiscence, which has a great impact in fertility. Moreover, the increased ovule number in the YPet-rgl2Δ17 line points out the role of RGL2 in the determination of ovule number.