ABSTRACT
In flowering plants, anther dehiscence and pollen release are essential for sexual reproduction. Anthers dehisce after cell wall degradation weakens stomium cell junctions in each anther locule, and desiccation creates mechanical forces that open the locules. Either effect or both together may break stomium cell junctions. The microRNA miR167 negatively regulates ARF6 and ARF8, which encode auxin response transcription factors. Arabidopsis mARF6 or mARF8 plants with mutated miR167 target sites have defective anther dehiscence and ovule development. Null mir167a mutations recapitulated mARF6 and mARF8 anther and ovule phenotypes, indicating that MIR167a is the main miR167 precursor gene that delimits ARF6 and ARF8 expression in these organs. Anthers of mir167a or mARF6/8 plants overexpressed genes encoding cell wall loosening functions associated with cell expansion, and grew larger than wild-type anthers did starting at flower stage 11. Experimental desiccation enabled dehiscence of miR167-deficient anthers, indicating competence to dehisce. Conversely, high humidity conditions delayed anther dehiscence in wild-type flowers. These results support a model in which miR167-mediated anther growth arrest permits anther dehiscence. Without miR167 regulation, excess anther growth delays dehiscence by prolonging desiccation.
Subject(s)
Flowers/growth & development , Flowers/genetics , MicroRNAs/physiology , Ovule/growth & development , Agrobacterium tumefaciens , Arabidopsis , Cell Survival/genetics , Cell Wall/metabolism , Dehydration/genetics , Dehydration/metabolism , Gene Expression Regulation, Plant , Ovule/genetics , Ovule/metabolism , Phenotype , Plants, Genetically Modified , Pollen/genetics , Pollen/metabolismABSTRACT
Wild potato species have substantial phenotypic and physiological diversity. Here, we report a comprehensive assessment of wild and cultivated potato species based on genomic analyses of 201 accessions of Solanum section Petota. We sequenced the genomes of these 201 accessions and identified 6 487 006 high-quality single nucleotide polymorphisms (SNPs) from 167 accessions in clade 4 of Solanum section Petota, including 146 wild and 21 cultivated diploid potato accessions with a broad geographic distribution. Genome-wide genetic variation analysis showed that the diversity of wild potatoes is higher than that of cultivated potatoes, and much higher genetic diversity in the agronomically important disease resistance genes was observed in wild potatoes. Furthermore, by exploiting information about known quantitative trait loci (QTL), we identified 609 genes under selection, including those correlated with the loss of bitterness in tubers and those involved in tuberization, two major domesticated traits of potato. Phylogenetic analyses revealed a north-south division of all species in clade 4, not just those in the S. brevicaule complex, and further supported S. candolleanum as the progenitor of cultivated potato and the monophyletic origin of cultivated potato in southern Peru. In addition, we analyzed the genome of S. candolleanum and identified 529 genes lost in cultivated potato. Collectively, the molecular markers generated in this study provide a valuable resource for the identification of agronomically important genes useful for potato breeding.