Abstract
The 7B-1 tomato (Solanum lycopersicum L. cv Rutgers) is a male-sterile mutant with enhanced tolerance to abiotic stress, which makes it a potential candidate for hybrid seed breeding and stress engineering. To underline the molecular mechanism regulating the male-sterility in 7B-1, transcriptomic profiles of the 7B-1 male-sterile and wild type (WT) anthers were studied using mRNA sequencing (RNA-Seq). In total, 768 differentially expressed genes (DEGs) were identified, including 132 up-regulated and 636 down-regulated transcripts. Gene ontology (GO) enrichment analysis of DEGs suggested a general impact of the 7B-1 mutation on metabolic processes, such as proteolysis and carbohydrate catabolic process. Sixteen candidates with key roles in regulation of anther development were subjected to further analysis using qRT-PCR and in situ hybridization. Cytological studies showed several defects associated with anther development in the 7B-1 mutant, including unsynchronized anther maturation, dysfunctional meiosis, arrested microspores, defect in callose degradation and abnormal tapetum development. TUNEL assay showed a defect in programmed cell death (PCD) of tapetal cells in 7B-1 anthers. The present study provides insights into the transcriptome of the 7B-1 mutant. We identified several genes with altered expression level in 7B-1 (including beta-1,3 glucanase, GA2oxs, cystatin, cysteine protease, pectinesterase, TA29, and actin) that could potentially regulate anther developmental processes, such as meiosis, tapetum development, and cell-wall formation/degradation.
Highlights
In flowering plants, male-fertility is a highly regulated process, which requires proper cellular differentiation in anthers and timely regulation of microsporogenesis
Using RNA-Seq, we identified a number of genes with potential key roles in regulation of anther development and microsporogenesis, which were differentially expressed between wild type (WT) and 7B-1 anthers
With release of microspores from the tetrads in WT anthers, callose was completely degraded as evidenced by lack of the signal, while it persisted around the arrested microspores in 7B-1 anthers (Fig 1C and 1F)
Summary
Male-fertility is a highly regulated process, which requires proper cellular differentiation in anthers and timely regulation of microsporogenesis. A polygalacturonase gene is the only well characterized gene known so far, which is responsible for male-sterile phenotype of ps-2 tomato mutant [1]. Male-sterile tomato mutants with desired agricultural traits are advantageous for hybrid seed breeding. Male-sterile mutants in tomato have been classified into functional, structural, and sporogenous classes [4]. Positional sterile-2 (ps-2) tomato is a functional male-sterile mutant with defected pollen dehiscence [1]. Microsporogenesis could break down during meiosis, formation of tetrads or separation of microspores. In male-sterile (ms) 3 and ms tomato mutants, pollen mother cells (PMC) collapse in pre-meiotic anthers [6]. In ms and ms1035 (allelic to ms10) tomato mutants, microsporogenesis beaks down at meiosis due to aberrant regulation of tapetal cells [4,7]
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