Flower movement induced by weather-dependent tropism

The project aims to elucidate the mechanisms and adaptive significances of the weather-driven flower movement of Arabidopsis helleri subsp. gemmifera, in which flowers face upwards and downwards in sunny and rainy weather, respectively. To identify genes that are upregulated specifically in the pedicels of downward- and upward-facing flowers under rainy and sunny conditions, respectively, we analysed transcriptomes of pedicels, leaves, and flowers under sunny and rainy conditions in a natural population in Hyogo Prefecture, Japan. Samples were collected from five individuals in the natural population for each weather condition between 2:30 and 3:30 pm. The results of transcriptome analyses indicated that the change in flower orientation is caused by tropisms of elongating flower pedicels. Combinations of circadian clock and light activate either phototropism of flower pedicels to make flowers upward-facing in sunny or gravitropism to make flowers downward-facing in rain. Additional qPCR analyses on the reciprocal gene expression patterns between adaxial and abaxial halves of pedicels indicate that the response occurs through auxin-based differential elongation. The upward- and downward-facing of flowers enhanced pollinator attraction and flower protection, respectively, and both increased reproductive successes. Our study is first to show that flower pedicel has weather-dependent tropism that functions to balance the antagonistic reproductive demands under changing weathers.