Abstract
Cytoplasmic male sterility (CMS) lines are widely used for hybrid production in Brassica napus. The Shaan2A CMS system is one of the most important in China and has been used for decades; however, the male sterility mechanism underlying Shaan2A CMS remains unknown. Here, we performed transcriptomic and proteomic analysis, combined with additional morphological observation, in the Shaan2A CMS. Sporogenous cells, endothecium, middle layer, and tapetum could not be clearly distinguished in Shaan2A anthers. Furthermore, Shaan2A anther chloroplasts contained fewer starch grains than those in Shaan2B (a near-isogenic line of Shaan2A), and the lamella structure of chloroplasts in Shaan2A anther wall cells was obviously aberrant. Transcriptomic analysis revealed differentially expressed genes (DEGs) mainly related to carbon metabolism, lipid and flavonoid metabolism, and the mitochondrial electron transport/ATP synthesis pathway. Proteomic results showed that differentially expressed proteins were mainly associated with carbohydrate metabolism, energy metabolism, and genetic information processing pathways. Importantly, nine gene ontology categories associated with anther and pollen development were enriched among down-regulated DEGs at the young bud (YB) stage, including microsporogenesis, sporopollenin biosynthetic process, and tapetal layer development. Additionally, 464 down-regulated transcription factor (TF) genes were identified at the YB stage, including some related to early anther differentiation such as SPOROCYTELESS (SPL, also named NOZZLE, NZZ), DYSFUNCTIONAL TAPETUM 1 (DYT1), MYB80 (formerly named MYB103), and ABORTED MICROSPORES (AMS). These results suggested that the sterility gene in the Shaan2A mitochondrion might suppress expression of these TF genes in the nucleus, affecting early anther development. Finally, we constructed an interaction network of candidate proteins based on integrative analysis. The present study provides new insights into the molecular mechanism of Shaan2A CMS in B. napus.
Highlights
Rapeseed (Brassica napus) is an important oil crop producing both edible oil and industrial materials such as lubricants and biodiesel
Transcriptomic and proteomic analyses suggested that Cytoplasmic male sterility (CMS) in Shaan2A is controlled by a complex regulatory network. To further elucidate this mechanism, we investigated known and predicted interactions among candidate proteins corresponding to our differentially expressed genes (DEGs) and differentially expressed proteins (DEPs); for example, transcription factor (TF) associated with anther differentiation and genes belonging to the anther and pollen development Gene Ontology (GO) categories mentioned above
CMS has been widely studied by transcriptomic and proteomic analysis in different species, including onion (Yuan et al, 2018), cotton (Suzuki et al, 2013; Yang et al, 2018), maize (Li et al, 2017), and rapeseed (An et al, 2014; Du et al, 2016). These studies revealed that cotton CMS-D8 lines have reduced ability to eliminate ROS (Yang et al, 2018), secretion and translocation of sporopollenin precursors is significantly down-regulated in cabbage R2P2CMS (Xing et al, 2018), and significant DEGs in rapeseed SaNa-1A CMS and pol CMS mostly participate in protein synthesis and metabolic pathways (An et al, 2014; Du et al, 2016)
Summary
Rapeseed (Brassica napus) is an important oil crop producing both edible oil and industrial materials such as lubricants and biodiesel. Heterosis is widely observed in B. napus, with excellent hybrids having yields over 30% higher than their parents (Radoev et al, 2008). CMS is a maternally inherited trait, which is largely resulting from rearrangements of mitochondrial DNA, which results in an inability to generate pollen or in abnormal pollen (Schnable and Wise, 1998; Horn et al, 2014). Four major CMS systems have been used in rapeseed production: nap CMS (Shiga and Baba, 1971), pol CMS (Fu, 1981), Ogu CMS (Ogura, 1968), and Shaan2A CMS (Li, 1980). Pol CMS and Shaan2A CMS are the most commonly used CMS systems in B. napus in terms of number of three-line hybrids and the area planted with these hybrids (Fu, 1995) Four major CMS systems have been used in rapeseed production: nap CMS (Shiga and Baba, 1971), pol CMS (Fu, 1981), Ogu CMS (Ogura, 1968), and Shaan2A CMS (Li, 1980). pol CMS and Shaan2A CMS are the most commonly used CMS systems in B. napus in terms of number of three-line hybrids and the area planted with these hybrids (Fu, 1995)
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