Developmental Biology

• Meristems described


  1672
• Description of a plant embryo

  1679
• Patterns in Plant Development

  1972
• Plant mutants reported


  1989
• Mechanisms of Plant Development

  2003
• Regulatory Genes


  Connect genetics and development
• Goal of plant developmental genetics

  To establish the "complete chain of events from primary gene activity to morphological differences"
• Genetic factors


  Affect the size, shape and structure of plants
• Hierarchies of gene interaction

  Certain groups of genes are coordinately regulated to accomplish a particular developmental program
• Meristem


  May be under the control of a master switch or regulator genes that regulate entire developmental programs
• Gene/Protein Nomenclature Guidelines


  Symbols for genes are italicized (e.g., IGF1), whereas symbols for proteins are not italicized (e.g., IGF1)
• All principal elements of the plant body are established by the heart stage of embryogenesis, approximately four days after fertilization
• Apical-to-basal transport of the hormone auxin is initiated at the early globular stage and plays a key role in defining the main axis of the embryo as well as promoting the formation of the central vasculature
• ARF


  Auxin response factor
• Aux/IAA


  Proteins that sequester and inactivate ARFs in the absence of an auxin signal
• Auxin signaling


  Aux/IAAs are rapidly degraded by the proteasome upon auxin signaling
• Auxin receptors


  TRANSPORTINHIBITOR RESPONSE1 (TIR1) and other members of the auxin signaling F-box (AFB) family, components of the SCF E3 ubiquitin ligase complex
• Auxin response


  Depends on the repertoire of ARF and Aux/IAA genes expressed in a given cell
• Polar auxin transport is a defining feature of plants
• Apical-to-basal auxin flux establishes and aligns cell polarity in the proembryo, thereby defining the main axis
• Auxin (IAA)


  Transported by a relay mechanism
• ARE


  Auxin response element in promoters, bound by ARF dimers
• Aux/IAAs


  Recruit TPL family corepressors, which in turn recruit chromatin modifying enzymes that stabilize the repressed state
• Auxin maxima always mark the positions of organ initiation and, later, of the tips of developing organ primordia
• PIN1


  Auxin efflux carrier that becomes preferentially localized to the basal membrane of the inner cells of the proembryo
• GN


  Required for the dynamic recycling of PIN proteins
• PIN proteins faithfully predict the flux of auxin, and pin mutants are impaired in auxin transport
• The distribution of PIN1 protein in the globular embryo marks not only an apical-basal polarity but also a central domain
• Canalization hypothesis


  Auxin acts to polarize its own transport, an important part of the mechanism that underlies coordinated tissue polarization
• DR5


  Synthetic auxin-responsive promoter driving the expression of a reporter gene, used to visualize or measure transcriptional responses to auxin and determine the position of auxin perception maxima
• WOX Family


  WUSCHEL (WUS) family of transcriptional factors involved in cell division, expansion and differentiation
• WUS expressing cells regulate the stem cell population of the SAM
• GNOM


  ARF guanine-nucleotide exchange factor (ARF-GEF) that regulates the formation of vesicles in membrane trafficking
• Mutations in GNOM/EMB30 (GN) result in seedlings that have no root, a short hypocotyl, and short, fused cotyledons
• GNOM is specifically involved in the endosomal recycling of the auxin-efflux carrier PIN1 to the basal plasma membrane in provascular cells, which is required for the accumulation of auxin at the future root pole
• YDA acts as part of a molecular switch to regulate extraembryonic or suspensor fate
• Auxin may play a role complementary to YDA and promotes normal development of the apical cell into a proembryo
• SHORT SUSPENSOR (SSP) and GROUNDED (GRD)


  Genes involved in suspensor formation, with SSP functioning in the YODA (YDA) mitogen-activated protein kinase pathway
• MONOPTEROS (MP)


  Auxin-responsive transcription factor required for primary root formation and vascular development
• Mutations that eliminate MP eliminate the embryonic axis, with cells at the base of the proembryo dividing abnormally and never elongating or becoming organized