AUTHOR=Wu jinxia , Zhang Zhiguo , Zhang QIan , Han Xiao , Gu Xiaofeng , Lu Tiegang 

TITLE=The molecular cloning and clarification of a photorespiratory mutant, oscdm1, using enhancer trapping

JOURNAL=Frontiers in Genetics

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2015.00226

DOI=10.3389/fgene.2015.00226

ISSN=1664-8021

ABSTRACT=<p>Enhancer trap systems have been demonstrated to increase the effectiveness of gene identification in rice. In this study, a <underline>c</underline>hlorophyll-<underline>d</underline>eficient <underline>m</underline>utant, named <italic>oscdm1</italic>, was screened and characterized in detail from a T-DNA enhancer-tagged population. The <italic>oscdm1</italic> plants were different from other chlorophyll-deficient mutants; they produced chlorotic leaves at the third leaf stage, which gradually died with further growth of the plants. However, the <italic>oscdm1</italic> plants were able to survive exposure to elevated CO<sub>2</sub> levels, similar to photorespiratory mutants. An analysis of the T-DNA flanking sequence in the <italic>oscdm1</italic> plants showed that the T-DNA was inserted into the promoter region of a serine hydroxymethyltransferase (SHMT) gene. OsSHMT1 is a key enzyme that is ubiquitous in nature and structurally conserved across kingdoms. The enzyme is responsible for the interconversion of serine and glycine and is essential for cellular one-carbon metabolism. Full-length <italic>OsSHMT1</italic> complemented the <italic>oscdm1</italic> phenotype, and the downregulation of <italic>OsSHMT1</italic> in wild-type plants by RNA interference (RNAi) produced plants that mimicked the <italic>oscdm1</italic> phenotype. GUS assays and quantitative PCR revealed the preferential expression of <italic>OsSHMT1</italic> in young leaves. TEM revealed serious damage to the thylakoid membrane in <italic>oscdm1</italic> chloroplasts. The <italic>oscdm1</italic> plants showed more extensive damage than wild type using an IMAGING-PAM fluorometer, especially under high light intensities. OsSHMT1-GFP localized exclusively to mitochondria. Further analysis revealed that the H<sub>2</sub>O<sub>2</sub> content in the <italic>oscdm1</italic> plants was twice that in wild type at the fourth leaf stage. This suggests that the thylakoid membrane damage observed in the <italic>oscdm1</italic> plants was caused by excessive H<sub>2</sub>O<sub>2</sub>. Interestingly, <italic>OsSHMT1</italic>-overexpressing plants exhibited increased photosynthetic efficiency and improved plant productivity. These results lay the foundation for further study of the <italic>OsSHMT1</italic> gene and will help illuminate the functional role of OsSHMT1 in photorespiration in rice.</p>