THE ROLES OF VANISHING TASSEL2 AND DEVELOPMENTAL DISASTER1 IN MAIZE VEGETATIVE AND INFLORESCENCE DEVELOPMENT

Open Access
- Author:
- Phillips, Kimberly Ann
- Graduate Program:
- Biology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 09, 2009
- Committee Members:
- Paula Mc Steen, Thesis Advisor/Co-Advisor
Paula Mc Steen, Thesis Advisor/Co-Advisor - Keywords:
- vanishing tassel2
tryptophan aminotransferase
Poaceae
plant hormone
mutation
meristem
maize
internode
inflorescence
indole-3-acetic acid
IAA
Developmental disaster1
development
bract
barren
auxin biosynthesis
auxin
vegetative
Zea mays - Abstract:
- Plant hormones control growth and development through the activity of genes that regulate their biosynthesis, transport, and response. Auxin has been found to play a crucial role in many aspects of growth, including cell division and expansion, flower development, adventitious root growth, tropisms, vascular development, and leaf phyllotaxy. Many genes that play a role in auxin-mediated growth and development have been identified in maize. In this thesis, the genetic regulation of maize vegetative and reproductive development will be examined, with a particular focus on the roles of auxin in these processes. The importance of polar auxin transport has previously been demonstrated in maize through the barren inflorescence2 (bif2) mutant. bif2 is co-orthologous to PINOID (PID) of Arabidopsis, which functions in the subcellular localization of the auxin efflux carrier PINFORMED1 (PIN1). pin, pid, and bif2 mutants all exhibit severe defects in reproductive development, including lack of flowers in pin and pid in Arabidopsis, and lack of branches and production of few or no spikelets in bif2 in maize. Another maize mutant, barren stalk1 (ba1), shows a reproductive phenotype similar to bif2, however ba1 mutants have been shown to transport auxin normally. ba1 was instead found to play a role in initiating an appropriate response to auxin, as mutants fail to initiate axillary meristems despite having the required levels of auxin at sites of meristem initiation. Finally, the maize mutant spi1 has recently been shown to function in auxin biosynthesis. spi1 mutants exhibit dramatic defects in both vegetative and reproductive development, including reduced height, leaf number, branch number, spikelet number, and kernel number. In Chapter 2, the characterization and cloning of vanishing tassel2 is presented. vt2 mutants resemble spi1 mutants, with defects in both vegetative and reproductive development. vt2;spi1 double mutants exhibit an additive genetic interaction, suggesting they function independently in maize development. Conversely, vt2;bif2 double mutants show a severely synergistic interaction in both vegetative and reproductive growth, indicating the crucial role of both auxin biosynthesis and auxin transport in maize development. Cloning of the vt2 locus has revealed that it encodes a tryptophan aminotransferase required for auxin biosynthesis. In Chapter 3, the characterization of the novel maize mutant Developmental disaster1 is presented. Unlike the other mutants described which are recessive, Dvd1 mutants are semidominant. Similar to vt2, Dvd1 mutants also show severe defects in vegetative and reproductive development. However, scanning electron microscopy reveals that Dvd1 inflorescence phenotypes share more similarity with ba1 mutants than with vt2. In addition, the genetic interaction of Dvd1 with bif2 has revealed that the two genes function independently in maize development, unlike the interaction of vt2 with bif2. Additional results, including current Dvd1 mapping data and genetic interactions with other maize mutants, are presented in Appendix A. Future positional cloning of the locus will reveal the nature of this mutation and further elucidate the critical role that Dvd1 plays in maize development. Characterization of the vt2 and Dvd1 phenotypes illustrates that mutants with similar severe defects in vegetative and reproductive development can have different underlying mechanisms. The cloning of vt2 is a significant contribution to the field since it reveals the importance of one of the Tryptophan-dependent auxin biosynthesis pathways for the first time in monocots. The mapping of Dvd1 provides the groundwork for its cloning in the future.