The Correlation of Symptom Development in Phyllody and Virescence with Gene Expressions in Floral Organ Identity and Pigment Synthesis and with Phytoplasma Accumulation in Phytoplasma-infected Catharanthus roseus
Date Issued
2010
Date
2010
Author(s)
Su, Yi-Ting
Abstract
Phytoplasmas infected periwinkles exhibit flower malformation, including petal discoloration, virescence, phyllody, witches’ broom, and other severe symptoms such as leaf yellowing, and stem proliferation. The flower malformation is a very unique symptom in phytoplasma-infected plants. Therefore, this research aims to elucidate how and why phytoplasma cause the special symptom. Because flower organ identity is regulated by A-class (AP1 and AP2), B-class (AP3 and PI), C-class (AG) and-E class gene (SEP) and flower pigment synthesis requires chalcone synthase (CHS) and chalcone isomerase (CHI), four floral organ identity genes, AP3, PI, AG and SEP3 and two pigment synthesis genes, CHS and CHI were analyzed using relative real time RT-PCR to compare the expression levels of those genes in three floral malformation stages of periwinkle infected with periwinkle leaf yellowing phytoplama (PLY phytoplasma) or peanut witches’ broom phytoplasma (PnWB phytoplasma). Expression of all floral organ identity genes and pigment synthesis genes was down-regulated. Suppression of AP3 gene followed the severity of floral malformation stages in both phytoplasma infected periwinkles. The suppression of PI gene was more severe in PnWB phytoplasma infected periwinkles than that in PLY phytoplasma infected plants. Trend of this suppression in PnWB phytoplasma infected periwinkles was similar to that of AP3 suppression. Suppression of AG gene did not follow with the severity of floral malformation stages in both phytoplasma infected periwinkles. SEP3 gene showed the most significant suppression among examined floral organ identity genes in malformed flowers. Suppression of SEP3 also followed the severity of floral malformation in PnWB infected periwinkle ; however, did not exhibit the same correlation with severity in PLY infected periwinkles. Supression of both pigment synthesis genes, CHS and CHI, was close in stage 2 and stage 3 in both phytoplasma infected periwinkles. The suppression of CHI gene is less severe than that of CHS gene. Phytoplasma titers of the defined stages were also determined in flowers and their surrounding leaves using absolute quantitative real time PCR. Following the severity of floral malformation, phytoplasma accumulation increased especially in malformed flowers. At the stage three, the phytoplasma titer was around 5 fold higher in the stage 3 malformed leaf-like flowers than that in leaves in PnWB phytoplasma infected periwinkles, and was more than three fold higher in PLY phytoplasma infected plants. These results indicate that the phyllody and virescence caused by phytoplasma infection are correlated with the down-regulation of floral organ identity genes and pigment synthesis genes in periwinkle, and also suggest that the flower to leaf conversion caused by phytoplasma infection significantly promote phytoplasma accumulation.
Subjects
floral organ identity genes
phyllody
pigment synthesis genes
real-time PCR
virescence
Type
thesis
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