UVM Theses and Dissertations
Format:
Print
Author:
Zhang, Yucan
Dept./Program:
Plant Biology
Year:
2014
Degree:
PhD
Abstract:
In addition to being used in photosynthesis, light also regulates the development of both the shoot and the root of plants. Although nodulation is a beneficial symbiosis between the plant and its rhizobial symbiont, it is energetically expensive.
We found that red light stimulates and far-red light inhibits nodulation of Medicago truncatula and other legumes, indicating the involvement of the phytochrome system. The giraffe mutant of M truncatula, isolated in our lab, has defects in response to red and far-red light and exhibits a classic photomorphogenic phenotype. We found that giraffe mutants are insensitive to both red light stimulation and far-red light inhibition of nodulation. Blue light also inhibits nodulation of alfalfa, pea and Lotus japonicus, but does not require the GIR gene.
In addition, we found that red light stimulates and enhances the induction of early nodulation genes such as ENODII and NIN. In contrast, blue light does not inhibit the induction of nodulation genes at early epidermal stage, but does inhibit Nod factor-induced gene expression later in the cortex, suggesting that blue light and red light regulate nodulation via different mechanisms. The nodulation of the L. japonicas astray mutant, which has a mutation in the homolog of the HY5 transcription factor, is insensitive to both red light stimulation and far-red light inhibition of nodulation, and partially insensitive to blue light inhibition, indicating interaction between the phytochrome and cryptochrome signaling pathways in the regulation of nodulation.
Nodulation of grafted plants showed that the GIR gene is required in the shoot to mediate red light stimulation of nodulation. This observation indicates the involvement of a secondary shoot-to-root signal in the light regulation of nodulation. Possible candidates are plant hormones such as abscisic acid (ABA), auxin, cytokinin, jasmonic acid and ethylene, which play a significant role in light signaling and regulation of nodulation.
We found that nodulation of the ethylene-insensitive mutant, sickle, is resistant to the inhibitory effect of far-red and blue light on nodulation, but responds normally to the stimulatory effect of red light. We also found that plants Insensitive or partially insensitive to ABA have defects in light regulation of nodulation, and our data suggest that ABA signaling is down-regulated by red light and up-regulated by blue light. Gene expresseion analysis revealed that light may regulate ethylene or ABA levels in plants by regulating the expression of their biosyntheticgenes. Since both ethylene and ABA have been shown to negatively regulate nodulation, our data suggest the involvelemnt of a complex plan hormone regulatory network that functions downstream of light to regulate nodulation.
We found that red light stimulates and far-red light inhibits nodulation of Medicago truncatula and other legumes, indicating the involvement of the phytochrome system. The giraffe mutant of M truncatula, isolated in our lab, has defects in response to red and far-red light and exhibits a classic photomorphogenic phenotype. We found that giraffe mutants are insensitive to both red light stimulation and far-red light inhibition of nodulation. Blue light also inhibits nodulation of alfalfa, pea and Lotus japonicus, but does not require the GIR gene.
In addition, we found that red light stimulates and enhances the induction of early nodulation genes such as ENODII and NIN. In contrast, blue light does not inhibit the induction of nodulation genes at early epidermal stage, but does inhibit Nod factor-induced gene expression later in the cortex, suggesting that blue light and red light regulate nodulation via different mechanisms. The nodulation of the L. japonicas astray mutant, which has a mutation in the homolog of the HY5 transcription factor, is insensitive to both red light stimulation and far-red light inhibition of nodulation, and partially insensitive to blue light inhibition, indicating interaction between the phytochrome and cryptochrome signaling pathways in the regulation of nodulation.
Nodulation of grafted plants showed that the GIR gene is required in the shoot to mediate red light stimulation of nodulation. This observation indicates the involvement of a secondary shoot-to-root signal in the light regulation of nodulation. Possible candidates are plant hormones such as abscisic acid (ABA), auxin, cytokinin, jasmonic acid and ethylene, which play a significant role in light signaling and regulation of nodulation.
We found that nodulation of the ethylene-insensitive mutant, sickle, is resistant to the inhibitory effect of far-red and blue light on nodulation, but responds normally to the stimulatory effect of red light. We also found that plants Insensitive or partially insensitive to ABA have defects in light regulation of nodulation, and our data suggest that ABA signaling is down-regulated by red light and up-regulated by blue light. Gene expresseion analysis revealed that light may regulate ethylene or ABA levels in plants by regulating the expression of their biosyntheticgenes. Since both ethylene and ABA have been shown to negatively regulate nodulation, our data suggest the involvelemnt of a complex plan hormone regulatory network that functions downstream of light to regulate nodulation.