UVM Theses and Dissertations
Format:
Print
Author:
Liang, Yan
Dept./Program:
Botany
Year:
2007
Degree:
PhD
Abstract:
The plant hormone abscisic acid (ABA) regulates numerous important aspects of plant development. We have identified a new plant response to the addition of ABA, increased lateral root formation in legumes, which is opposite to that observed in nonlegumes. Legumes are unique due to the ability to form symbiotic root nodules with Rhizobium. Phylogenetic studies based on the sequence of rbcL gene indicate that all nodule-forming plants belong to a single clade Rosid I, suggesting a predisposition for nodulation evolved early in the history of the legume lineage. In our study, the acquisition of altered responsiveness of roots to ABA is coincident with the appearance of a predisposition for nodulation within the legumes, followed by a loss in Chamaecrista. These data suggest the existence of an altered ABA signaling pathway in legume roots that is related to the ability to form nitrogen-fixing nodules.
I found that the LATD gene of the model legume, Medicago truncatula, is a key component of ABA signaling in legume roots. In latd mutants, primary root growth eventually arrests, resulting in a disorganized root tip lacking a presumptive meristem and root cap columella cells. Lateral root organs are more severely affected; latd lateral roots arrest immediately after emerging from the primary root, and reveal a lack of organization. We demonstrate that the plant hormone, ABA, can rescue the latd root, but not nodule, meristem defects. latd mutants have normal levels of ABA, but exhibit reduced sensitivity to the hormone in two other ABA-dependent processes: seed germination and stomatal closure. Together, these observations demonstrate that the latd mutant is defective in the ABA response and indicate a role for LATD-dependent ABA signaling in M. truncatula root meristem function.
In order to identify the components of LATD-dependent ABA signaling in M truncatula, we looked for homologs of ABA responsive genes from arabidopsis and tomato. I identified homologs of three ABA responsive genes that we named MtAREBI, MtABI8, MtASRl. The transcript levels of all three homologs are induced by the addition of ABA in leaves and root tips. In addition, I found that the expression of the MtASRI and MfABI8 genes is regulated by the LATD gene in roots, but not in leaves, whereas the MtAREBl gene is induced by exogenous ABA by a LATD-independent signaling pathway in both leaves and roots. These data provide evidence for a LATD-dependent branch of the ABA signaling pathway in M truncatula roots.
So far, I have mapped LATD to a small interval of less than 1 cM. My results indicate that LATD is 0.05 cM from the marker 003CO1 on the telomeric side and 0.6 cM from the marker 7m9-03 on the centromeric side of chromosome 1. No recombination events were observed between LATD and marker 164n9. These results lay the groundwork for the future cloning of the LATD gene. The research presented here enhances our understanding of the correlation between lateral root and nodule development in M. truncatula, as well as the role of ABA on the root apical meristem.
I found that the LATD gene of the model legume, Medicago truncatula, is a key component of ABA signaling in legume roots. In latd mutants, primary root growth eventually arrests, resulting in a disorganized root tip lacking a presumptive meristem and root cap columella cells. Lateral root organs are more severely affected; latd lateral roots arrest immediately after emerging from the primary root, and reveal a lack of organization. We demonstrate that the plant hormone, ABA, can rescue the latd root, but not nodule, meristem defects. latd mutants have normal levels of ABA, but exhibit reduced sensitivity to the hormone in two other ABA-dependent processes: seed germination and stomatal closure. Together, these observations demonstrate that the latd mutant is defective in the ABA response and indicate a role for LATD-dependent ABA signaling in M. truncatula root meristem function.
In order to identify the components of LATD-dependent ABA signaling in M truncatula, we looked for homologs of ABA responsive genes from arabidopsis and tomato. I identified homologs of three ABA responsive genes that we named MtAREBI, MtABI8, MtASRl. The transcript levels of all three homologs are induced by the addition of ABA in leaves and root tips. In addition, I found that the expression of the MtASRI and MfABI8 genes is regulated by the LATD gene in roots, but not in leaves, whereas the MtAREBl gene is induced by exogenous ABA by a LATD-independent signaling pathway in both leaves and roots. These data provide evidence for a LATD-dependent branch of the ABA signaling pathway in M truncatula roots.
So far, I have mapped LATD to a small interval of less than 1 cM. My results indicate that LATD is 0.05 cM from the marker 003CO1 on the telomeric side and 0.6 cM from the marker 7m9-03 on the centromeric side of chromosome 1. No recombination events were observed between LATD and marker 164n9. These results lay the groundwork for the future cloning of the LATD gene. The research presented here enhances our understanding of the correlation between lateral root and nodule development in M. truncatula, as well as the role of ABA on the root apical meristem.