Functional genetics of rice PISTILLATA genes reveals new roles and target genes in flowering time, female fertility and parthenocarpy
Diversification of transcription factors and of their downstream targets can contribute to new organ morphologies. An example is rice lodicule, a small fleshy petal analogue that aids floret opening, thus facilitates pollination and fertility. To understand the mechanism underlying its specification, we investigated the developmental functions of the rice PISTILLATA (PI) paralogs, OsMADS2 and OsMADS4. Null osmads2 mutants reiterated OsMADS2 nonredundant lodicule specification roles and importantly revealed new roles in flowering time and floral organ number and fate in multiple whorls. Doubly perturbed <i>osmads2d8/d8 osmads4kd</i> florets had severe abnormalities and initiated parthenocarpy. Remarkably, ubiquitous OsMADS4 overexpression rescued osmads2 abnormalities, though impaired anther development and seed setting. Target genes whose (in)direct regulation can contribute to OsMADS2 functions were discovered by identifying its genome-wide binding regions and by transcriptome profiling. Several OsMADS2 targets are implicated in lodicule and stamen development, floral organ number, cell wall, cell shape and osmotic homeostasis processes. Altogether, we reveal novel roles for the rice PI paralogs, e.g. panicle exsertion and embryo sac differentiation and provide mechanistic insights on their diversification and functions in floral organ specification. Overall design: Genome wide binding of OsMADS2 transcription factor in rice genome by high throughput sequencing and downstream analysis