Abstract
BackgroundChemical hybridization agents (CHAs) are often used to induce male sterility for the production of hybrid seeds. We previously discovered that monosulfuron ester sodium (MES), an acetolactate synthase (ALS) inhibitor of the herbicide sulfonylurea family, can induce rapeseed (Brassica napus L.) male sterility at approximately 1% concentration required for its herbicidal activity. To find some clues to the mechanism of MES inducing male sterility, the ultrastructural cytology observations, comparative transcriptome analysis, and physiological analysis on carbohydrate content were carried out in leaves and anthers at different developmental stages between the MES-treated and mock-treated rapeseed plants.ResultsCytological analysis revealed that the plastid ultrastructure was abnormal in pollen mother cells and tapetal cells in male sterility anthers induced by MES treatment, with less material accumulation in it. However, starch granules were observed in chloroplastids of the epidermis cells in male sterility anthers. Comparative transcriptome analysis identified 1501 differentially expressed transcripts (DETs) in leaves and anthers at different developmental stages, most of these DETs being localized in plastid and mitochondrion. Transcripts involved in metabolism, especially in carbohydrate and lipid metabolism, and cellular transport were differentially expressed. Pathway visualization showed that the tightly regulated gene network for metabolism was reprogrammed to respond to MES treatment. The results of cytological observation and transcriptome analysis in the MES-treated rapeseed plants were mirrored by carbohydrate content analysis. MES treatment led to decrease in soluble sugars content in leaves and early stage buds, but increase in soluble sugars content and decrease in starch content in middle stage buds.ConclusionsOur integrative results suggested that carbohydrate and lipid metabolism were influenced by CHA-MES treatment during rapeseed anther development, which might responsible for low concentration MES specifically inducing male sterility. A simple action model of CHA-MES inducing male sterility in B. napus was proposed. These results will help us to understand the mechanism of MES inducing male sterility at low concentration, and might provide some potential targets for developing new male sterility inducing CHAs and for genetic manipulation in rapeseed breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1388-5) contains supplementary material, which is available to authorized users.
Highlights
Chemical hybridization agents (CHAs) are often used to induce male sterility for the production of hybrid seeds
We previously found that monosulfuron ester sodium (MES) can induce complete male sterility in rapeseed at a concentration below 1% of that required for its herbicide activity and it has no significant influence on plant vegetative growth [8]
Cytological studies reveal that MES treatment affects the plastid ultrastructure and metabolite accumulation in the developing anthers We previously showed that MES treatment causes two typical defects in sterile anthers: type I with early broken down tapetum at the pollen mother cell (PMC) stage and type II with abnormal nondegraded tapetum at the mature pollen stage [8]
Summary
Chemical hybridization agents (CHAs) are often used to induce male sterility for the production of hybrid seeds. In 1950, it was reported that the plant growth regulator maleic hydrazide can induce male sterility in corn plants [4,5] This initial finding led to the induction of male sterility by a chemical hybridization agent (CHA), which became an important tool for crop heterosis. The availability of safe and selective chemicals capable of inducing male sterility without causing any significant adverse effect on plant growth and development has been the necessary prerequisite in the pursuit of this approach. We previously found that monosulfuron ester sodium (MES) can induce complete male sterility in rapeseed at a concentration below 1% of that required for its herbicide activity and it has no significant influence on plant vegetative growth [8]
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