Abstract
The signal from organelle to nucleus, namely retrograde regulation of nuclear gene expression, was largely unknown. Due to the nuclear-cytoplasmic incompatibility in cytoplasmic male-sterile (CMS) plants, we employed CMS Brassica juncea to investigate the retrograde regulation of nuclear gene expression in this study. We studied how reduced BjRCE1 gene expression caused by the nuclear-cytoplasmic incompatibility altered the auxin response in CMS of B. juncea. We isolated the BjRCE1 gene that was located in the nucleus from B. juncea. Over-expression of BjRCE1 enhanced auxin response in transgenic Arabidopsis. The expression of BjRCE1 was significantly reduced in CMS compared with its maintainer fertile (MF) line of B. juncea. There were fewer lateral roots in CMS than MF under normal and treatment of indole-3-acetic acid (IAA) conditions. Expression patterns of several auxin-related genes together with their phenotypes indicated a reduced auxin response in CMS compared to MF. The phenotypes of auxin response and auxin-related gene expression pattern could be mimicked by inhibiting mitochondrial function in MF. Taken together, we proposed reduced expression of BjRCE1 gene modulated by nuclear-cytoplasmic incompatibility alters auxin response in CMS B. juncea. This may be an important mechanism of retrograde regulation of nuclear gene expression in plants.
Highlights
In plant cells, mitochondria and chloroplast are semi-autonomous organelles that encode some genetic information, with the majority being derived and imported from the nucleus
Plastid retrograde regulation (PRR) was relatively well described, in which the GUN1 gene integrated the multiple indicators in plastid and led to ABI4mediated the repression of nuclear gene expression [6]
Expression Patterns of Auxin-related Genes in maintainer fertile (MF), cytoplasmic male-sterile (CMS) We studied the expressions of auxin-related genes including auxin efflux carrier (PIN2 and PIN3), auxin-responsive GH3 family protein (GH3), efflux carrier of polar auxin transport (PAT), ARFlike small GTPase (GTP) and subunit of SCF complex (Cullin) in MF, CMS and MF/CMS treated with indole-3-acetic acid (IAA) of B. juncea
Summary
Mitochondria and chloroplast are semi-autonomous organelles that encode some genetic information, with the majority being derived and imported from the nucleus. There has been increasing attention paid to studies of signals from the nucleus to organelles, termed ‘anterograde regulation’ due to the predominant role of the nucleus in the cell, which has mainly focused on pentatricopeptide repeat (PPR) proteins that regulate RNA editing in mitochondria and chloroplast and the male fertile restorer (Rf) gene in CMS lines [1,2,3]. Mitochondrial retrograde regulation (MRR) of nuclear gene expression was first investigated in yeast [7] and has been well described in yeasts and mammals (reviewed by [8]). Plastid retrograde regulation (PRR) was relatively well described, in which the GUN1 gene integrated the multiple indicators in plastid and led to ABI4mediated the repression of nuclear gene expression [6]
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