Research On The Roles Of Arabidopsis CRF Family In Root Development & The Relationship Between Rice Crown Root Number And Auxin

Auxin and cytokinin are important plant growth hormones. During plant root development, cytokinin promotes cell differentiation through inhibiting auxin signaling, whereas auxin sustains meristem activity through promoting cell division. Together they determine the size of root meristem and root growth.CRF family is a subfamily of AP2/ERF family. Several members of CRF family are involved in cytokinin pathway, pest-resistance and salt-stress responses. Development of cotyledon, leaf and embryo are known to be regulated by CRF genes.In this study, we used a number of developmental cell biological approaches and obtained the following results:1. Quantification analysis of root length, meristem size and meristematic cortex cell number showed that crf3 mutants have reduced meristematic cortex cell number and thus shorter root meristem and length.2. Quantification of cortex cell number in the root meristem at 22℃and 28℃showed that higher temperature reduced cell number in meristem in Arabidopsis. Cell number in the root meristem of crf3-5 was affected at 28℃but not 22℃.3. Quantification of cortex cell number in the root meristem at 22℃and 28℃after zeatin treatment showed that sensitivity of the same crf mutants to zeatin varied in different temperature. This indicates that temperature influences cytokinin response in crfs4. 2.4-D treatment of crfs showed that crf2-1, crf3-5, crf3-6 were more sensitive than wild type. This implies that CRFs is related to auxin.In summary, CRFs regulate cell number in the root meristem, influence meristem size to detemine root length. CRFs are related to both cytokinin and auxin in root development, and their function are regulated by temperature. Different allelic mutant have different root phenotypes, which may result from different insertion sites.Rice root system is genetically diverse. However the number of varieties used in rice root system research is small until now, the differences of rice root system in different varieties are still largely unknown. Rice has a fibrous root system, which mainly consists of crown roots essential for absorbing nutrition and water. Auxin is known to regulate the number of rice crown roots, but how different rice varieties response to auxin and auxin transport inhibition is still unknown.To address this we used an improved rice root experimental system and obtained a number of results listed below:1. An improved rice root experimental system was established, which can be used for high-throughput phenotypic analysis of rice crown root.2. Localized NPA treatment at root-shoot conjunction (RSO) caused no differences in GUS staining at coleoptile, but GUS staining at RSO was lower at higher NPA concentration. These indicate that a reduction of auxin level at RSO will lead to less crown roots. At the same time, we found that different rice cultivars have different NPA sensitivity. we thus hypothesized that auxin homeostasis in different ecotypes are different.3. Removal of root tip caused more crown roots, whereas shoot decapitation caused less crown roots. These indicate that both auxin under and above ground are related to crown root number.4. NPA treatment at the middle position of root showed that at high NPA concentration, crown root became less; whereas in low NPA concentration, ZS97 had more crown roots. These indicate that auxin in RSO comes from the root tip, and a reduction of auxin derived from root tip will lead to less crown roots.5. Time course analysis of root length after NPA treatment in RSO from 1d-4d showed that at low concentration root growth were not inhibited by NPA. At high concentration, however, root growth was inhibited. These imply that inhibition of auxin transport will retard root growth.Taken together, in this study, I measured 42 rice cultivars for a core rice collection, and confirmed that rice crown root has genetical diversity. I analyzed the sensitivity of crown root number to auxin, and studied the mechanism of rice crown root formation. My results showed that the number of rice crown root is controlled by the level of auxin at RSO, which is determined by auxin transported from both above and under ground parts.