Chlorosis of Ogura-CMS Brassica rapa is due to down-regulation of genes for chloroplast proteins

Abstract

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Abstract Cytoplasmic male sterility (CMS) is a maternally inherited trait leading to loss of the ability to produce fertile pollen and is extensively used in hybrid crop breeding. Ogura-CMS was originally generated by insertion of orf138 upstream of atp8 in the radish mitochondrial genome and transferred to Brassica crops for hybrid breeding. Gene expression changes by dysfunctional mitochondria in Ogura-CMS result in pollen developmental defects, but little is known about gene expression patterns in vegetative tissue. To examine the interaction between nuclear and organellar regulation of gene expression, microarray and subsequent gene expression experiments were conducted with leaves of F 1 hybrid Chinese cabbage derived from selfincompatible (SI) or Ogura-CMS parents (Brassica rapa ssp. pekinensis). Out of 24,000 genes deposited on a KBGP24K microarray, 66 genes were up-regulated and 26 genes were down-regulated by over 2.5 fold in the CMS leaves. Up-regulated genes included stress-response genes and mitochondrial protein genes, while genes for ascorbic acid biosynthesis and thylakoid proteins were down-regulated. Most of the major component genes for light reactions of photosynthesis were highly expressed in leaves of both SI and CMS plants, but most of the corresponding proteins were found to be greatly reduced in leaves of CMS plants, indicating posttranscriptional regulation. Reduction in thylakoid proteins and chlorophylls led to reduction in photosynthetic efficiency and chlorosis of Ogura-CMS at low temperatures. This research provides a foundation for studying chloroplast function regulated by mitochondrial signal and for using organelle genome introgression in molecular breeding.

Mechanism and Utilization of Ogura Cytoplasmic Male Sterility in Cruciferae Crops

“…Microsporocytes give rise to pollen via meiosis, and somatic cells, particularly tapetal cells, are essential for the normal development and release of pollen [ 167 ]. The failure to produce functional pollen in Ogura CMS lines is found to be accompanied by DEGs involved in microspore formation, anther development, pollen wall formation, exine formation (the formation and dissolution of the callose wall, fatty acid metabolism pathway and biosynthesis of sporopollenin precursors in the tapetum), the accumulation of the pollen coat and pectinesterase activity [ 159 , 160 , 161 , 163 , 164 , 165 , 166 , 167 , 168 ]. CMS always induces the expression of stress-related genes, especially HSP genes [ 160 , 162 , 164 , 168 , 169 ].…”

“…The failure to produce functional pollen in Ogura CMS lines is found to be accompanied by DEGs involved in microspore formation, anther development, pollen wall formation, exine formation (the formation and dissolution of the callose wall, fatty acid metabolism pathway and biosynthesis of sporopollenin precursors in the tapetum), the accumulation of the pollen coat and pectinesterase activity [ 159 , 160 , 161 , 163 , 164 , 165 , 166 , 167 , 168 ]. CMS always induces the expression of stress-related genes, especially HSP genes [ 160 , 162 , 164 , 168 , 169 ]. ORF138 may affect redox status in Ogura CMS plants, although only DEG evidence exists [ 159 , 160 , 164 ].…”