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Background Numerous regulatory genes participate in plant thermotolerance. In Arabidopsis, HEAT-INDUCED TAS1 TARGET2 (HTT2) is an important thermotolerance gene that is silenced by ta-siR255, a trans-acting siRNA. ta-siR255 is absent from heading Chinese cabbage (Brassica rapa ssp. pekinensis). Our previous attempt to overexpress the endogenous BrpHTT2 gene of heading Chinese cabbage (B. rapa ssp. pekinensis) failed because of cosuppression. In theory, heading Chinese cabbage can overexpress Arabidopsis HTT2 to improve thermotolerance in the absence of ta-siR255-mediated gene silencing and the weak potential of coexpression. Results To test the potential application of HTT2 in improving crop thermotolerance, we transferred p35S::HTT2 to heading Chinese cabbage. We tested the leaf electrical conductivity, hypocotyl elongation, and survival percentage of p35S::HTT2 plants subjected to high-temperature (38 °C) and heat-shock (46 °C) treatment. The leaf electrical conductivity of p35S::HTT2 seedlings under high temperature decreased but did negligibly change under heat shock. The hypocotyl length of p35S::HTT2 seedlings increased under high temperature and heat shock. The survival rate of p35S::HTT2 seedlings increased under heat shock. BrpHsfs, a subset of heat-shock factor genes, were upregulated in p35S::HTT2 plants under high-temperature and heat shock conditions. In the field, transgenic plants with HTT2 appeared greener and formed leafy heads earlier than wild-type plants. Conclusions Exogenous HTT2 increased the survival rates of heat-shocked heading Chinese cabbage by promoting thermotolerance through decreasing electrical conductivity and extending hypocotyl length. Our work provides a new approach to the genetic manipulation of thermotolerance in crops through the introduction of exogenous thermotolerance genes. Electronic supplementary material The online version of this article (10.1186/s12870-018-1346-x) contains supplementary material, which is available to authorized users.

microRNAs (miRNAs) are a class of newly identified, noncoding, small RNA molecules that negatively regulate gene expression. Many miRNAs are reportedly involved in plant growth, development and stress response processes. However, their roles in the sexual reproduction mechanisms in flowering plants remain unknown. Pollen development is an important process in the life cycle of a flowering plant, and it is closely related to the yield and quality of crop seeds. This study aimed to identify miRNAs involved in pollen development. A microarray assay was conducted using the known complementary sequences of plant miRNAs as probes on inflorescences of a sterile male line (Bcajh97-01A) and a fertile male line (Bcajh97-01B) of the Brassica campestris ssp. chinensis cv. ‘Aijiaohuang’ genic male sterility sister line system (Bcajh97-01A/B). The results showed that 44 miRNAs were differently expressed in the two lines. Of these, 15 had over 1.5-fold changes in their transcript levels, with 9 upregulated and 6 downregulated miRNAs in inflorescences of ‘Bcajh97-01A’ sterile line plants. We then focused on 3 of these 15 miRNAs (miR158, miR168 and miR172). Through computational methods, 13 family members were predicted for these 3 miRNAs and 22 genes were predicted to be their candidate target genes. By using 5’ modified RACE, 2 target genes of miR168 and 5 target genes of miR172 were identified. Then, qRT-PCR was applied to verify the existence and expression patterns of the 3 miRNAs in the flower buds at five developmental stages. The results were generally consistent with those of the microarray. Thus, this study may give a valuable clue for further exploring the miRNA group that may function during pollen development. Electronic Supplementary Material Supplementary material is available for this article at 10.2478/s11658-013-0097-9 and is accessible for authorized users.

Background microRNAs (miRNAs) are endogenous, noncoding, small RNAs that have essential regulatory functions in plant growth, development, and stress response processes. However, limited information is available about their functions in sexual reproduction of flowering plants. Pollen development is an important process in the life cycle of a flowering plant and is a major factor that affects the yield and quality of crop seeds. Results This study aims to identify miRNAs involved in pollen development. Two independent small RNA libraries were constructed from the flower buds of the male sterile line (Bcajh97-01A) and male fertile line (Bcajh97-01B) of Brassica campestris ssp. chinensis. The libraries were subjected to high-throughput sequencing by using the Illumina Solexa system. Eight novel miRNAs on the other arm of known pre-miRNAs, 54 new conserved miRNAs, and 8 novel miRNA members were identified. Twenty-five pairs of novel miRNA/miRNA* were found. Among all the identified miRNAs, 18 differentially expressed miRNAs with over two-fold change between flower buds of male sterile line (Bcajh97-01A) and male fertile line (Bcajh97-01B) were identified. qRT-PCR analysis revealed that most of the differentially expressed miRNAs were preferentially expressed in flower buds of the male fertile line (Bcajh97-01B). Degradome analysis showed that a total of 15 genes were predicted to be the targets of seven miRNAs. Conclusions Our findings provide an overview of potential miRNAs involved in pollen development and interactions between miRNAs and their corresponding targets, which may provide important clues on the function of miRNAs in pollen development.