An Ethylene Over-Producing Mutant of Tomato (<i>Solanum lycopersicum</i>), Epinastic, Exhibits Tolerance to High Temperature Conditions

Above-optimal temperatures reduce yield in many crops, including tomato, largely because of the heat-sensitivity of their reproduction process. A full understanding of heat-stress (HS) response and thermotolerance of tomato reproduction is still lacking. Recently, using external application of the plant hormone ethylene, it was demonstrated that ethylene plays a role in heat-tolerance of tomato pollen (the male reproductive cells). In order to expand our understanding on involvement of ethylene in tomato pollen thermotolerance, we analyzed the response of wild type and ethylene-related tomato mutant plants to HS, at physiological and molecular levels. We report that mild chronic HS conditions highly reduce the number of viable and germinating pollen grains as well as the production of seeded fruits in wild type tomato plants, while no significant reduction was detected/observed in pollen quality, number of seeded fruits and seeds per fruit in plants of the ethylene over-producer mutant epinastic. Our findings suggest that ethylene is involved in thermotolerance of tomato reproduction, pointing to an effect on pollen viability and germination potential, highlighting candidate genes involved in pollen response to HS (like SlHSP17, SlHSP101, SlMBF1) and suggesting directions for further studies.

Increased branching independent of strigolactone in cytokinin oxidase 2-overexpressing tomato is mediated by reduced auxin transport

Tomato production is influenced by shoot branching,which is controlled by different hormones.Here we produced tomato plants overexpressing the cytokinin-deactivating gene CYTOKININ OXYDASE 2(CKX2).CKX2-overexpressing(CKX2-OE)plants showed an excessive growth of axillary shoots,the opposite phenotype expected for plants with reduced cytokinin content,as evidenced by LC-MS analysis and ARR5-GUS staining.The TCP transcription factor SlBRC1b was downregulated in the axillary buds of CKX2-OE and its excessive branching was dependent on a functional version of the GRAS-family gene LATERAL SUPPRESSOR(LS).Grafting experiments indicated that increased branching in CKX2-OE plants is unlikely to be mediated by root-derived signals.Crossing CKX2-OE plants with transgenic antisense plants for the strigolactone biosynthesis gene CAROTENOID CLEAVAGE DIOXYGENASE(CCD7-AS)produced an additive phenotype,indicating independent effects of cytokinin and strigolactones on increased branching.On the other hand,CKX2-OE plants showed reduced polar auxin transport and their bud outgrowth was reduced when combined with auxin mutants.Accordingly,CKX2-OE basal buds did not respond to auxin applied in the decapitated apex.Our results suggest that tomato shoot branching depends on a fine-tuning of different hormonal balances and that perturbations in the auxin status could compensate for the reduced cytokinin levels in CKX2-OE plants.