RNA sequencing of laser-capture microdissected compartments of the maize kernel identifies regulatory modules associated with endosperm cell differentiation

Endosperm is an absorptive structure that supports embryo development or seedling germination in angiosperms. The endosperm of cereals is a main source of food, feed, and industrial raw materials worldwide. However, the genetic networks that regulate endosperm cell differentiation remain largely unclear. As a first step toward characterizing these networks, we profiled the mRNAs in five major cell types of the differentiating endosperm and in the embryo and four maternal compartments of the maize (Zea mays) kernel. Comparisons of these mRNA populations revealed the diverged gene expression programs between filial and maternal compartments and an unexpected close correlation between embryo and the aleurone layer of endosperm. Gene coexpression network analysis identified coexpression modules associated with single or multiple kernel compartments including modules for the endosperm cell types, some of which showed enrichment of previously identified temporally activated and/or imprinted genes. Detailed analyses of a coexpression module highly correlated with the basal endosperm transfer layer (BETL) identified a regulatory module activated by MRP-1, a regulator of BETL differentiation and function. These results provide a high-resolution atlas of gene activity in the compartments of the maize kernel and help to uncover the regulatory modules associated with the differentiation of the major endosperm cell types.

Dynamic microtubules and endomembrane cycling contribute to polarity establishment and early development of Ectocarpus mitospores

Many zygotes and spores of brown algae are photosensitive and establish a developmental axis in accordance with directional light cues. Ectocarpus siliculosus is being advanced as a genetic and genomic model organism for investigating brown alga development, and this report investigates photopolarization of the growth axis of mitospores. When exposed to unidirectional light, mitospores photopolarized and established a growth axis such that germination was preferentially localized to the shaded hemisphere of the spore body. The roles of the microtubule cytoskeleton and endomembrane cycling in the photopolarization process were investigated using pharmacological agents. Disruption of microtubule dynamics progressively reduced the percentage of mitospores that photopolarized, while inhibition of vesicle secretion blocked photopolarization nearly completely. Chronic treatment with these pharmacological agents severely affected algal morphogenesis. Microtubules in mitospores and algal filaments were imaged by confocal microscopy. Mitospores contained a radial microtubule array, emanating from a centrosome associated with the nuclear envelope. At germination, the radial array gradually transitioned into a longitudinal array with microtubules extending into the emerging apex. At mitosis, spindles were aligned with the growth axis of cylindrical cells in the filament, and the division plane bisected the spindle axis. These studies demonstrate that dynamic membrane cycling and microtubule assembly play fundamental roles in photopolarization and provide a foundation for future genetic and genomic investigations of this important developmental process.