Characterization of the cellular and molecular defects induced by the boron deficiency mimic phenylboronic acid in the primary root of maize

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Deficiency of the micronutrient boron is a widespread abiotic stress leading to drastic yield reductions in many crops, including maize. The underlying molecular causes are only partially understood. Boron is accessible to plants in form of boric acid and the key in understanding boron function lies in its ability to bind to cis-diol groups. Although there are many potential binding partners of boron within a plant cell, it has only been shown to bind to and more importantly to crosslink two Rhamnogalacturonan-II molecules in the cell wall. Whether there are additional binding partners of boron and whether boron outside the cell wall is of biological importance are open questions in the field. To address these questions, the proposed project will make use of the chemical phenylboronic acid (PBA), which is a boric acid analog. Like boric acid, PBA still delivers boron into the cell and can bind to cis-diol groups. Unlike boric acid, PBA cannot cross link molecules and is therefore used to induce boron-deficiency like defects. PBA has the potential to identify additional functions of boron despite its crosslinking function and additional binding partners of boron. The proposed project will characterize the cellular and molecular defects induced by PBA in the maize primary root and will compare them to defects induced by boron deficiency. Special emphasis will be put on cell division, cell expansion, meristem development, ethylene biosynthesis, auxin transport and cytokinin signaling. Additionally, the proposed project will identify targets of PBA through forward chemical screening and proteomics approaches.