The role of barren inflorescence genes, barren inflorescence2 (bif2), barren stalk1 (ba1)and suppressor of sessile spikelet1 (sos1), in maize inflorescence development

Open Access
Author:
Wu, Xianting
Graduate Program:
Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 06, 2008
Committee Members:
  • Paula Mc Steen, Committee Chair
  • Hong Ma, Committee Member
  • Zhi Chun Lai, Committee Member
  • Kathleen Marie Brown, Committee Member
Keywords:
  • barren inflorescence
  • maize
  • inflorescence development
Abstract:
ABSTRACT There are four types of axillary meristem initiated during maize inflorescence development. Thus, the structure of the maize inflorescence is quite different from Arabidopsis which has two types of axillary meristems. Other grass species such as rice, sorghum and wheat have similar inflorescence morphology. More importantly, as the inflorescence produces the seed, the increase in the complexity of the grass inflorescence has caused an increase in yield. Grass species are the main food source for human beings. Therefore, it is very important to understand the development of the grass inflorescence. In addition, the development of the grass inflorescence involves hormonal regulation. There are many advantages to choosing the maize inflorescence as a model system to study grass inflorescence development such as the large meristem size to perform hormone analysis, the multiple types of axillary meristem as well as the established genetic and genomic resources. Therefore, maize is a good system to perform research on inflorescence development and hormonal regulation. In my work described in chapter 2, I provide support that polar auxin transport (PAT) is required for initiation of axillary meristems in the maize inflorescence such as the branch meristem (BM), spikelet pair meristem (SPM) and spikelet meristem (SM). In addition, RNA in situ hybridization analysis showed the interaction of two important barren inflorescence genes, barren inflorescence2 (bif2) and barren stalk1 (ba1), with PAT. bif2 and ba1 mutants have defects in the initiation of all axillary meristems. The role of bif2 appears to be similar to PINOID (PID) in Arabidopsis which regulates auxin transport to initiate axillary meristems in the inflorescence. However, as ba1 homologs are absent in Arabidopsis genome, bif2 regulation of ba1 may shed light in understanding the unique aspects of maize inflorescence development and signal transduction network. My analysis of bif2;ba1 double mutants in chapter 3 showed that the interaction between bif2 and ba1 is complex. My work together with others has shown that regulation occurs at both the transcription and post transcription level. This is consistent with the model we proposed in the chapter 2. In addition, we revise our model to account for all of the evidence from genetic and molecular analysis. This will provide information to further test the interaction between bif2 and ba1. In chapter 4, I characterized Suppressor of sessile spikelet1 (Sos1) and its interaction with ramosa1 (ra1) and ramosa2 (ra2). Since these three genes are involved in determining SPM determinacy, their interaction determines the mature architecture of the maize inflorescence. We proposed a model based on all the molecular and genetic analysis which helps to understand how these three genes interact and function in maize meristem determinacy. Cloning of the Sos1 gene will be very important to understand how the maize inflorescence produces paired spikelets instead of single spikelets. This is an important derived trait in grass inflorescence evolution. In addition, I showed in chapter 2 that blocking auxin transport in early development phenocopies the Sos1 mutant phenotype. This indicates that Sos1 may be involved in the auxin signal transduction pathway to regulate maize inflorescence development. The progress towards cloning sos1 is shown in Appendix A. Although our understanding of maize inflorescence development is ongoing, my research provides clues to understand some of the main players such as bif2, ba1, PAT, Sos1, ra1 and ra2. In addition, my analysis primarily defines the positions of these genes in the network. By further analysis based on these models, we will understand more of the cross talk between these genes to control maize inflorescence development.