Abstract Background Extreme weather events are predicted to increase, such as combined heat and drought. The CO 2 concentration ([CO 2 ]) is predicted to approximately double by 2100. We aim to explore how tomato physiology, especially photosynthesis, is affected by combined heat and drought under elevated [CO 2 ] (e [CO 2 ]). Results Two genotypes, ‘OuBei’ (‘OB’, Solanum lycopersicum ) and ‘LA2093’ ( S. pimpinellifolium ) were grown at a [CO 2 ] (atmospheric [CO 2 ], 400 ppm) and e [CO 2 ] (800 ppm), respectively. The 27-days-old seedlings were treated at 1) a [CO 2 ], 2) a [CO 2 ] + combined stress, 3) e [CO 2 ] and 4) e [CO 2 ] + combined stress, followed by recovery. The P N (net photosynthetic rate) increased at e [CO 2 ] as compared with a [CO 2 ] and combined stress inhibited the P N . Combined stress decreased the F v /F m (maximum quantum efficiency of photosystem II) of ‘OB’ at e [CO 2 ] and that of ‘LA2093’ in regardless of [CO 2 ]. Genotypic difference was observed in the e [CO 2 ] effect on the gas exchange, carbohydrate accumulation, pigment content and dry matter accumulation. Conclusions Short-term combined stress caused reversible damage on tomato while the e [CO 2 ] alleviated the damage on photosynthesis. However, the e [CO 2 ] cannot be always assumed have positive effects on plant growth during stress due to increased water consumption. This study provided insights into the physiological effects of e [CO 2 ] on tomato growth under combined stress and contributed to tomato breeding and management under climate change.
A dominant suppressor of the ABAR overexpressor, soar1-1D, from CHLH/ABAR [coding for Mg-chelatase H subunit/putative abscisic acid (ABA) receptor (ABAR)] overexpression lines was screened to explore the mechanism of the ABAR-mediated ABA signalling. The SOAR1 gene encodes a pentatricopeptide repeat (PPR) protein which localizes to both the cytosol and nucleus. Down-regulation of SOAR1 strongly enhances, but up-regulation of SOAR1 almost completely impairs, ABA responses, revealing that SOAR1 is a critical, negative, regulator of ABA signalling. Further genetic evidence supports that SOAR1 functions downstream of ABAR and probably upstream of an ABA-responsive transcription factor ABI5. Changes in the SOAR1 expression alter expression of a subset of ABA-responsive genes including ABI5. These findings provide important information to elucidate further the functional mechanism of PPR proteins and the complicated ABA signalling network.
Abstract MicroRNAs (miRNAs) are 19–24 nucleotide (nt) noncoding RNAs that play important roles in abiotic stress responses in plants. High temperatures have been the subject of considerable attention due to their negative effects on plant growth and development. Heat-responsive miRNAs have been identified in some plants. However, there have been no reports on the global identification of miRNAs and their targets in tomato at high temperatures, especially at different elevated temperatures. Here, three small-RNA libraries and three degradome libraries were constructed from the leaves of the heat-tolerant tomato at normal, moderately and acutely elevated temperatures (26/18 °C, 33/33 °C and 40/40 °C, respectively). Following high-throughput sequencing, 662 conserved and 97 novel miRNAs were identified in total with 469 conserved and 91 novel miRNAs shared in the three small-RNA libraries. Of these miRNAs, 96 and 150 miRNAs were responsive to the moderately and acutely elevated temperature, respectively. Following degradome sequencing, 349 sequences were identified as targets of 138 conserved miRNAs, and 13 sequences were identified as targets of eight novel miRNAs. The expression levels of seven miRNAs and six target genes obtained by quantitative real-time PCR (qRT-PCR) were largely consistent with the sequencing results. This study enriches the number of heat-responsive miRNAs and lays a foundation for the elucidation of the miRNA-mediated regulatory mechanism in tomatoes at elevated temperatures.
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