Hormonal Regulation of Leaf Morphogenesis in Arabidopsis

Leaf morphogenesis is strictly controlled not only by intrinsic genetic factors, such as transcriptional factors, but also by environmental cues, such as light, water and pathogens. Nevertheless, the molecular mechanism of how leaf morphogenesis is regulated by genetic programs and environmental cues is far from clear. Numerous series of events demonstrate that plant hormones, mostly small and simple molecules, play crucial roles in plant growth and development, and in responses of plants to environmental cues such as light. With more and more genetics and molecular evidence obtained from the model plant Arabidopsis, several fundamental aspects of leaf morphogenesis including the initiation of leaf primordia, the determination of leaf axes, the regulation of cell division and expansion in leaves have been gradually unveiled. Among these phytohormones, auxin is found to be essential in the regulation of leaf morphogenesis.

Leaf morphogenesis:The multifaceted roles of mechanics

Plants produce a rich diversity of biological forms,and the diversity of leaves is especially notable.Mechanisms of leaf morphogenesis have been studied in the past two decades,with a growing focus on the interactive roles of mechanics in recent years.Growth of plant organs involves feedback by mechanical stress:growth induces stress,and stress affects growth and morphogenesis.Although much attention has been given to potential stress-sensing mechanisms and cellular responses,the mechanical principles guiding morphogenesis have not been well understood.Here we synthesize the overarching roles of mechanics and mechanical stress in multilevel and multiple stages of leaf morphogenesis,encompassing leaf primordium initiation,phyllotaxis and venation patterning,and the establishment of complex mature leaf shapes.Moreover,the roles of mechanics at multiscale levels,from subcellular cytoskeletal molecules to single cells to tissues at the organ scale,are articulated.By highlighting the role of mechanical buckling in the formation of three-dimensional leaf shapes,this review integrates the perspectives of mechanics and biology to provide broader insights into the mechanobiology of leaf morphogenesis.

Development of Rice Leaves:How Histocytes Modulate Leaf Polarity Establishment

An ideal leaf shape is beneficial to the yield of rice.Molecular understanding of the leaf primordia and polarity establishment plays a significant role in exploring the genetic regulatory network of leaf morphogenesis.In recent years,researchers have cloned an array of coding genes and a few non-coding small RNAs involved in rice leaf development through regulating the development of leaf primordia,vascular bundles,sclerenchyma cells,bulliform cells,cell walls and epidermis cells.These genes and their interactions play critical roles in rice leaf development through the determination and regulatory role in gene expression,and their coordination with other genetic networks or signal pathways.But the relationship among these genes is poorly defined and the underlying network is still unclear.In this review,we introduced the regulatory pathways of leaf primordium development and leaf polarity establishment,mainly the relationship between cell development mechanism and leaf polarity establishment,focusing on how leaf tissue affects leaf shape.Hopefully,the regulation network reviewed here has immediate implications for future research and genomic design breeding.

Genome of Plant Maca （Lepidium meyenil） Illuminates Genomic Basis for High-Altitude Adaptation in the Central Andes

Maca （Lepidium meyenii Walp, 2n = 8x = 64）, belonging to the Brassicaceae family, is an economic plant cultivated in the central Andes sierra in Peru （4000-4500 m）. Considering that the rapid uplift of the central Andes occurred 5-10 million years ago （Ma）, an evolutionary question arises regarding how plants such as maca acquire high-altitude adaptation within a short geological period. Here, we report the high-quality genome assembly of maca, in which two closely spaced maca-specific whole-genome duplications （WGDs; ~6.7 Ma） were identified. Comparative genomic analysis between maca and closely related Brassicaceae species revealed expansions of maca genes and gene families involved in abiotic stress response, hormone signaling pathway, and secondary metabolite biosynthesis via WGDs. The retention and subsequent functional divergence of many duplicated genes may account for the morphological and physiological changes （i.e., small leaf shape and self-fertility） in maca in a high-altitude environment. In addition, some duplicated maca genes were identified with functions in morphological adaptation （i.e., LEAF CURLING RESPONSIVENESS） and abiotic stress response （i.e., GL YClNE-RICH RNA-BINDING PROTEINS and DNA-DAMAGE-REPAIR/TOLERATION2） under positive selection. Collectively, the maca genome provides use- ful information to understand the important roles of WGDs in the high-altitude adaptation of plants in the Andes.