Genetic analysis of stem development in Arabidopsis thaliana.
Published: 2004
Language: eng
Number of pages: 218
Description: This study assesses features of Arabidopsis inflorescence stem and pedicel development and begins to genetically dissect the mechanisms driving morphogenesis and differentiation patterns. Pedicels were found to consist of two regions with different developmental origins: a proximal stalk representing the majority of the elongated organ and a distal bulge that emerges from the flower base. Outgrowth of the bulge requires activity of the  BREVIPEDICELLUS (BP) gene, and in bp mutants distal pedicels are radially constricted around their circumferences. Mutant radial constrictions extend further proximally on abaxial and lateral sides of pedicels, leading to occasional downward bending at the distal pedicel. This effect is severely enhanced in a loss-of-function erecta (er) background, resulting in radially constricted tissue along the entire abaxial side of pedicels and downward-oriented flowers and fruit bp er morphological defects were accompanied by a loss of cortical chlorenchyma as well as small epidermal cells and no stomata on abaxial sides of pedicels. Analysis of mutant inflorescence stems revealed that similar cell patterns project as stripes down internodes from bases of leaves and pedicels. Moreover, wild-type nodes display achlorophyllous regions adjacent to lateral organs, suggesting that altered differentiation patterns in bp er pedicels and internodes may be due to expansion of nodal features into underlying stems. Differentiation defects in mutant pedicels and stems parallel vascular bundle patterns, strongly implicating a vasculature-associated factor in the regulation of the phenotype. Cloning the BP gene revealed that it encodes a class I KNOTTED-like homeodomain protein previously invoked in the regulation of apical meristem activity. BP is expressed in cortical regions throughout stems and pedicels and is upregulated at nodes adjacent to lateral organs. Collectively, the bp mutant phenotype, identity of the  BP gene product and the expression pattern suggest that  BP meristematic function has been co-opted by stems to maintain a growth-competent state during development. Molecular analysis of a suppressor of bp er showing elongated, perpendicular pedicels demonstrated that the FILAMENTOUS FLOWER gene was mutated. A well-established role for FIL in promotion of lateral organ abaxial identity indicates that dorsiventral organ symmetry may impinge on the development of stems.
Notes: Adviser:  C. D. Riggs.

Botany theses.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 4935.