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Ronzan, M.; Piacentini, D.; Fattorini, L.; Federica, D. R.; Caboni, E.; Eiche, E.; Ziegler, J.; Hause, B.; Riemann, M.; Betti, C.; Altamura, M. M.; Falasca, G. Auxin-jasmonate crosstalk in Oryza sativa L. root system formation after cadmium and/or arsenic exposure Environ Exp Bot 165, 59-69, (2019) DOI: 10.1016/j.envexpbot.2019.05.013

Soil pollutants may affect root growth through interactions among phytohormones like auxin and jasmonates. Rice is frequently grown in paddy fields contaminated by cadmium and arsenic, but the effects of these pollutants on jasmonates/auxin crosstalk during adventitious and lateral roots formation are widely unknown. Therefore, seedlings of Oryza sativa cv. Nihonmasari and of the jasmonate-biosynthetic mutant coleoptile photomorphogenesis2 were exposed to cadmium and/or arsenic, and/or jasmonic acid methyl ester, and then analysed through morphological, histochemical, biochemical and molecular approaches.In both genotypes, arsenic and cadmium accumulated in roots more than shoots. In the roots, arsenic levels were more than twice higher than cadmium levels, either when arsenic was applied alone, or combined with cadmium. Pollutants reduced lateral root density in the wild -type in every treatment condition, but jasmonic acid methyl ester increased it when combined with each pollutant. Interestingly, exposure to cadmium and/or arsenic did not change lateral root density in the mutant. The transcript levels of OsASA2 and OsYUCCA2, auxin biosynthetic genes, increased in the wild-type and mutant roots when pollutants and jasmonic acid methyl ester were applied alone. Auxin (indole-3-acetic acid) levels transiently increased in the roots with cadmium and/or arsenic in the wild-type more than in the mutant. Arsenic and cadmium, when applied alone, induced fluctuations in bioactive jasmonate contents in wild-type roots, but not in the mutant. Auxin distribution was evaluated in roots of OsDR5::GUS seedlings exposed or not to jasmonic acid methyl ester added or not with cadmium and/or arsenic. The DR5::GUS signal in lateral roots was reduced by arsenic, cadmium, and jasmonic acid methyl ester. Lipid peroxidation, evaluated as malondialdehyde levels, was higher in the mutant than in the wild-type, and increased particularly in As presence, in both genotypes.Altogether, the results show that an auxin/jasmonate interaction affects rice root system development in the presence of cadmium and/or arsenic, even if exogenous jasmonic acid methyl ester only slightly mitigates pollutants toxicity.

Kowalski, A. M.; Gooding, M.; Ferrante, A.; Slafer, G. A.; Orford, S.; Gasperini, D.; Griffiths, S. Agronomic assessment of the wheat semi-dwarfing gene Rht8 in contrasting nitrogen treatments and water regimes Field Crop Res 191, 150-160, (2016) DOI: 10.1016/j.fcr.2016.02.026

Reduced height 8 (Rht8) is the main alternative to the GA-insensitive Rht alleles in hot and dry environments where it reduces plant height without yield penalty. The potential of Rht8 in northern-European wheat breeding remains unclear, since the close linkage with the photoperiod-insensitive allele Ppd-D1a is unfavourable in the relatively cool summers. In the present study, two near-isogenic lines (NILs) contrasting for the Rht8/tall allele from Mara in a UK-adapted and photoperiod-sensitive wheat variety were evaluated in trials with varying nitrogen fertiliser (N) treatments and water regimes across sites in the UK and Spain.The Rht8 introgression was associated with a robust height reduction of 11% regardless of N treatment and water regime and the Rht8 NIL was more resistant to root-lodging at agronomically-relevant N levels than the tall NIL. In the UK with reduced solar radiation over the growing season than the site in Spain, the Rht8 NIL showed a 10% yield penalty at standard agronomic N levels due to concomitant reduction in grain number and spike number whereas grain weight and harvest index were not significantly different to the tall NIL. The yield penalty associated with the Rht8 introgression was overcome at low N and in irrigated conditions in the UK, and in the high-temperature site in Spain. Decreased spike length and constant spikelet number in the Rht8 NIL resulted in spike compaction of 15%, independent of N and water regime. The genetic interval of Rht8 overlaps with the compactum gene on 2DS, raising the possibility of the same causative gene. Further genetic dissection of these loci is required.Abbreviations    ANOVA, analysis of variance; Y, yield; HI, harvest index; GN, grain number (m−2); SS, spikelet number (spike−1); SN, spike number (m−2); HD, heading date; AN, anthesis; 12L, length of the second internode from the top; 13L, length of the third internode from the top; PAR, photosynthetically active radiation; R: FR, red: far-red light reflectance ratio; RCBD, randomised complete block design
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