A novel RNA binding protein affects rbcL gene expression and is specific to bundle sheath chloroplasts in C4plantsReportar como inadecuado

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BMC Plant Biology

, 13:138

Biochemistry and physiology


BackgroundPlants that utilize the highly efficient C4 pathway of photosynthesis typically possess kranz-type leaf anatomy that consists of two morphologically and functionally distinct photosynthetic cell types, the bundle sheath BS and mesophyll M cells. These two cell types differentially express many genes that are required for C4 capability and function. In mature C4 leaves, the plastidic rbcL gene, encoding the large subunit of the primary CO2 fixation enzyme Rubisco, is expressed specifically within BS cells. Numerous studies have demonstrated that BS-specific rbcL gene expression is regulated predominantly at post-transcriptional levels, through the control of translation and mRNA stability. The identification of regulatory factors associated with C4 patterns of rbcL gene expression has been an elusive goal for many years.

ResultsRLSB, encoded by the nuclear RLSB gene, is an S1-domain RNA binding protein purified from C4 chloroplasts based on its specific binding to plastid-encoded rbcL mRNA in vitro. Co-localized with LSU to chloroplasts, RLSB is highly conserved across many plant species. Most significantly, RLSB localizes specifically to leaf bundle sheath BS cells in C4 plants. Comparative analysis using maize C4 and Arabidopsis C3 reveals its tight association with rbcL gene expression in both plants. Reduced RLSB expression through insertion mutation or RNA silencing, respectively led to reductions in rbcL mRNA accumulation and LSU production. Additional developmental effects, such as virescent-yellow leaves, were likely associated with decreased photosynthetic function and disruption of associated signaling networks.

ConclusionsReductions in RLSB expression, due to insertion mutation or gene silencing, are strictly correlated with reductions in rbcL gene expression in both maize and Arabidopsis. In both plants, accumulation of rbcL mRNA as well as synthesis of LSU protein were affected. These findings suggest that specific accumulation and binding of the RLSB binding protein to rbcL mRNA within BS chloroplasts may be one determinant leading to the characteristic cell type-specific localization of Rubisco in C4 plants. Evolutionary modification of RLSB expression, from a C3 -default- state to BS cell-specificity, could represent one mechanism by which rbcL expression has become restricted to only one cell type in C4 plants.

KeywordsC4 photosynthesis S1-domain RNA binding protein rbcL gene expression Cell-type specificity Post transcriptional control C4 maize C3Arabidopsis AbbreviationsBSBundle sheath

LSULarge subunit of Rubisco


NAD-MENAD dependent malic enzyme

NADP-MENADP dependent malic enzyme

PEPCasePhosphoenolpyruvate carboxylase

PPRPentatricopeptide repeat

PSIIIPhotosystem III

RLSBrbcL RNA S1-binding domain protein

RubiscoRibulose-1,5-bisphosphate carboxylase-oxygenase

RuBPRibulose bisphosphate

SSUSmall subunit of Rubisco.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2229-13-138 contains supplementary material, which is available to authorized users.

Shaun M Bowman, Minesh Patel, Pradeep Yerramsetty contributed equally to this work.

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Fuente: https://link.springer.com/

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