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Latex-containing cells called laticifers are present in at least 41 flowering plant families and are thought to have convergently evolved at least 12 times. These cells are known to function in defense, but little is known about the molecular genetic mechanisms of their development. The expansion of laticifers into their distinctive tube shape can occur through two distinct mechanisms, cell fusion and intrusive growth. The mechanism and extent of intrusive laticifer growth are still being investigated. Hormonal regulation by jasmonic acid and ethylene is important for both laticifer differentiation and latex biosynthesis. Current evidence suggests that laticifers can be specified independently of latex production, but extensive latex production requires specified laticifers. Laticifers are an emerging system for studying the intersection of cell identity specification and specialized metabolism.

In flowering plants, sexual reproduction culminates in double fertilization, which occurs after an ovule receives two sperm cells from a single pollen tube. Recent progress in pollen tube guidance, as well as analyses of fertilization-defective mutants, have highlighted a post-fertilization event that rapidly terminates pollen tube attraction. This event plays a crucial role in ensuring a one-to-one fertilization system between males and females. This phenomenon is controlled by the activity of persistent synergid cells, which secrete peptides that attract and thus guide the pollen tube. This review briefly introduces new findings on cell biology and signaling pathways that regulate the unique inactivation mechanism of persistent synergid cells.

Mobile transcription factors play essential roles in plant development including the control of cell identity and tissue patterning, as well as organ initiation and the induction of major developmental switches. Within the past few years, the molecules and cellular structures that regulate the movement of these signals have emerged. Here we cover some of the major findings of the past two years as they relate to the intercellular movement of multiple different families of transcription factors.

Pattern formation of the early Arabidopsis embryo generates precursors to all major cell types, and is profoundly controlled by the signaling molecule auxin. Here we discuss recent milestones in our understanding of auxin-dependent embryo patterning. Auxin biosynthesis, transport and response mechanisms interact to generate local auxin accumulation in the early embryo. New auxin-dependent reporters help identifying these sites, while atomic structures of transcriptional response mediators help explain the diverse outputs of auxin signaling. Key auxin outputs are control of cell identity and cell division orientation, and progress has been made towards understanding the cellular basis of each. Importantly, a number of studies have combined computational modeling and experiments to analyze the developmental role, genetic circuitry and molecular mechanisms of auxin-dependent cell division control.

www.sciencedirect.com In this issue we cut a broad section through the information provided by a variety of approaches ranging from the analysis of whole organs to molecular studies on the most basic aspects of cell growth, division, and identity. We find that our understanding of processes as fundamental as alternation of generations, organ formation, cell polarity, cell identity, responses to environmental cues, and the shift from vegetative to reproductive growth is advancing rapidly. Several of the articles in this issue note parallels between pathways utilized for developmental control in plants and animals and these comparisons promise to aid in understanding their evolutionary origins.