Publikationen - Molekulare Signalverarbeitung

The phytohormone auxin is a potent regulator of plant development. Since its discovery in the beginning of the twentieth century many aspects of auxin biology have been extensively studied, ranging from biosynthesis and metabolism to the elucidation of molecular components of downstream signaling. With the identification of the F-box protein TIR1 as an auxin receptor a major breakthrough in understanding auxin signaling has been achieved and recent modeling approaches have shed light on the putative mechanisms underlying the establishment of auxin gradients and maxima essential for many auxin-regulated processes. Here, we review these and other recent advances in unraveling the entanglement of biosynthesis, polar transport and cellular signaling events that allow small auxinic molecules to facilitate their complex regulatory action.

Ribonuclease LE (RNaseLE) from tomato (Lycopersicon esculentum Mill. cv. Lukullus) belongs to the widespread RNase T2 family of ribonucleases. With the exception of S-RNases of the solanaceous self-incompatibility system the functions of other members of the RNase T2 family are only barely understood. Using a 2.6-kbp putative promoter sequence of RNaseLE in front of the uidA reporter gene, expression of β-glucuronidase in developing phloem tissue and, especially, in the meristematic and elongation zones at root tips was detected. The tissue-specific expression accords with the range of cis-acting elements detected in the RNaseLE promoter. RNaseLE mRNA was localized in developing phloem cells but not in mature phloem tissue, suggesting association of RNaseLE expression with phloem development. Histochemical staining of β-glucuronidase activity as well as detailed inspection of RNaseLE at mRNA, protein and enzyme activity levels revealed that the wound-induced expression of RNaseLE was also restricted to vascular tissue. RNaseLE transcript accumulation detected by in situ hybridization occurred preferentially in phloem and cambial cells of stem sections upon wounding. The data provide evidence for a role of RNaseLE in a tissue-specific wound response and in wound healing of tomato.