Min Ni

We study light-regulated de-etiolation responses downstream of plant photoreceptors. We also explore Arabidopsis seed development. We take protein interaction, genetic, epigenetic, and genomic approaches.

Red/far-red light-absorbing phytochromes and blue/UV-A light-absorbing cryptochromes regulate seedling de-etiolation. PIF4 is a critical signaling hub downstream of the photoreceptors as well as temperature and hormonal regulatory pathways. Its expression peaks in the morning and afternoon. Excess light toward noon damages the photosynthetic apparatus and plants need a balanced photomorphogenesis to avoid photodamage. Upregulation of PIF4 expression by the interaction of SHB1 with the circadian clock proteins CCA1/LHY under red light represents a desensitization step. We study how SHB1 and CCA1/LHY regulate PIF expression after dawn. As noon approaches and ambient temperature tends to increase, the SHB1-CCA1 interaction sustains PIF4 expression to trigger plant thermomorphogenic responses. Moreover, we also study proteins that work together with PIF4 regulating thermomorphogenesis and mechanisms that repress PIF4 expression toward evening.

Double fertilization in angiosperms leads to the formation of a diploid embryo and a triploid endosperm. Seed development in Arabidopsis and some dicots undergoes an initial phase of active endosperm proliferation followed by a second phase in which embryo grows at the expense of the endosperm. In many dicots, the embryo grows to full size and the mature seed contains only a single layer of endosperm cells. However, excess endosperm proliferation always enlarges the final mature seeds. We study how endosperm proliferation is triggered by a few key genes such as IKU2, a LRR receptor protein kinase. IKU2 is specifically expressed in Arabidopsis endosperm at 2 to 3 Days after Pollination (DAP) and is then repressed at 4 to 5 DAP. Its activation is likely through an epigenetic mechanism. By contrast, IKU2 is continuously expressed in Brachypodium and rice. Second, we explore how IKU2 expression is repressed after 4 to 5 DAP for a phase transition to embryo development. Last, seed development in major seed crops such as soybean and canola follows a very similar path as Arabidopsis. Enhancing the potential for large seed sizes represents one of the most promising and less explored avenues for significant increases in agricultural yields.