Maize stigmas react differently to self-/cross-pollination and fungal invasion

During sexual reproduction in flowering plants, rapid tip-growing pollen tubes travel from the stigma inside the maternal tissues of the pistil towards ovules. In maize, the stigma is highly elongated forming thread-like strands known as silks. Only compatible pollen tubes are supported to penetrate and to grow successfully through the transmitting tract of the silk to reach the ovules. Like pollen, fungal spores germinate at the surface of silks and generate tube-like structures (hyphae) penetrating silk tissue. To elucidate commonalities and differences between silk responses to various invaders, we compared growth behavior of the various invaders as well as the silk transcriptome after self-pollination, cross-pollination and infection using two different fungi. We report that self-pollination triggers especially senescence genes, while incompatible pollination using Tripsacum dactyloides leads to downregulation of rehydration genes, microtubule and modulation of cell wall-related genes explaining slower pollen tube growth and their arrest. Invasion by the ascomycete Fusarium graminearum triggers numerous defense responses including the activation of monolignol biosynthesis and NAC as well as WRKY transcription factor genes, while responses to the basidiomycete Ustilago maydis are generally much weaker. Cell wall and phytoalexin biosynthesis pathways were selected as examples to demonstrate usability of the data sets provided.