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Summary: MicroRNAs (miRNAs) play crucial roles in regulating plant development and stress responses. However, the functions and mechanism of intronic miRNAs in plants are poorly understood.This study reports a stress‐responsive RNA splicing mechanism for intronic miR400 production, whereby miR400 modulates reactive oxygen species (ROS) accumulation and improves plant tolerance by downregulating its target expression.To monitor the intron splicing events, we used an intronic miR400 splicing‐dependent luciferase transgenic line. Luciferase activity was observed to decrease after high cadmium concentration treatment due to the retention of the miR400‐containing intron, which inhibited the production of mature miR400. Furthermore, we demonstrated that under Cd treatments, Pentatricopeptide Repeat Protein 1 (PPR1), the target of miR400, acts as a positive regulator by inducing ROS accumulation. Ppr1 mutation affected the Complex III activity in the electron transport chain and RNA editing of the mitochondrial gene ccmB.This study illustrates intron splicing as a key step in intronic miR400 production and highlights the function of intronic miRNAs as a 'signal transducer' in enhancing plant stress tolerance. [ABSTRACT FROM AUTHOR]

Mitogen-activated protein kinase ( MAPK) cascades are involved in plant development, stress responses and hormonal signal transduction. MAPK kinases ( MAPKKs), as the key nodes in these cascades, link MAPKs and MAPKK kinases ( MAPKKKs). In this study, Gh MKK4, a novel group C MAPKK gene from cotton ( Gossypium hirsutum), was isolated and identified. Its expression can be induced by various stresses and signalling molecules. The overexpression of GhMKK4 in Nicotiana benthamiana enhanced its susceptibility to bacterial and fungal pathogens, but had no significant effects on salt or drought tolerance. Notably, the overexpressing plants showed increased sensitivity to abscisic acid ( ABA) and gibberellin A3 ( GA3), and ABA and gibberellin ( GA) signalling were affected on infection with Ralstonia solanacearum bacteria. Furthermore, the overexpressing plants showed more reactive oxygen species ( ROS) accumulation and stronger inhibition of catalase ( CAT), a ROS-scavenging enzyme, than control plants after salicylic acid ( SA) treatment. Interestingly, two genes encoding ornithine decarboxylase ( ODC) and S-adenosylmethionine decarboxylase ( SAMDC), the key enzymes in polyamine synthesis, exhibited reduced R. solanacearum-induced expression in overexpressing plants. These findings broaden our knowledge about the functions of MAPKKs in diverse signalling pathways and the negative regulation of disease resistance in the cotton crop. [ABSTRACT FROM AUTHOR]

The molecular mechanism for sensing and transducing the stress signals initiated by K deprivation in plants remains unknown. Here, we found that the expression of AtHELPS, an Arabidopsis DExD/H box RNA helicase gene, was induced by low-K, zeatin and cold treatments, and downregulated by high-K stress. To further investigate the expression pattern of AtHELPS, pAtHELPS::GUS transgenic plants were generated. Histochemical staining indicated that AtHELPS is mainly expressed in the young seedlings and vascular tissues of leaves and roots. Using both helps mutants and overexpression lines, we observed that, in the low-K condition, AtHELPS affected Arabidopsis seed germination and plant weight. Interestingly, the mRNA levels of AKT1, CBL1/9 and CIPK23 in the helps mutants were much higher than in the overexpression lines under low-K stress. Moreover, under low-K stress, the helps mutants displayed increased K influx, whereas the overexpression line of AtHELPS had a lower flux rate in the roots by the noninvasive micro-test technique. Taken together, these results provide information for the functional analysis of plant DEVH box RNA helicases, and suggest that AtHELPS, as an important negative regulator, plays a role in K deprivation stress. The Arabidopsis DExD/H box RNA helicase gene, AtHELPS, was mainly expressed in young seedlings and vascular tissues of leaves and roots. It was also induced by low potassium stress and down-regulated by high potassium stress. In the low potassium condition AtHELPS affected Arabidopsis seed germination and plant weight by affecting transcription of AKT1, CBL1/9 and CIPK23 and K influx rate [ABSTRACT FROM AUTHOR]

Mitogen-activated protein kinase (MAPK) cascades play important roles in mediating pathogen responses and reactive oxygen species signaling. In plants, MAPKs are classified into four major groups (A-D). Previous studies have mainly focused on groups A and B, but little is known about group C. In this study, we functionally characterized a stress-responsive group C MAPK gene ( GhMPK2) from cotton. Northern blot analysis indicated that GhMPK2 was induced not only by signaling molecules, such as ethylene and methyl jasmonate, but also by methyl viologen-mediated oxidative stress. Transgenic tobacco ( Nicotiana tabacum) plants that overexpress GhMPK2 displayed enhanced resistance to fungal and viral pathogens, and the expression of the pathogenesis-related (PR) genes, including PR1, PR2, PR4, and PR5, was significantly increased. Interestingly, the transcription of 1-aminocyclopropane-1-carboxylic acid synthase ( ACS) and 1-aminocyclopropane-1-carboxylic acid oxidase ( ACO) was significantly upregulated in transgenic plants, suggesting that GhMPK2 positively regulates ethylene synthesis. Moreover, overexpression of GhMPK2 elevated the expression of several antioxidant enzymes, conferring on transgenic plants enhanced reactive oxygen species scavenging capability and oxidative stress tolerance. These results increased our understanding of the role of the group C GhMPK2 gene in multiple defense-signaling pathways, including those that are involved in responses to pathogen infection and oxidative stress. In this study, functional characterization of a cotton group C mitogen-activated protein kinase (MAPK) gene ( GhMPK2) was carried out. The expression of GhMPK2 was induced by signaling molecules and oxidative stress. Overexpression of GhMPK2 significantly elevated the expression of the pathogenesis-related ( PR), signaling-related and antioxidative genes, and thereby enhanced the transgenic plants disease resistance and oxidative stress tolerance. [ABSTRACT FROM AUTHOR]

Currently, the molecular regulation mechanisms involved in the early development of maize brace root are poorly known. To gain insight into the transcriptome dynamics that are associated with its development, genome-wide gene expression profiling was conducted by Solexa sequencing (Illumina Inc., San Diego, CA, USA). More than five million tags were generated from the stem node tissues without and with just-emerged brace roots, including 149 524 and 178 131 clean tags in the two libraries, respectively. Of these, 82 864 (55.4%) and 91 678 (51.5%) tags were matched to the reference genes. The most differentially expressed tags with a log ratio > 2 or < −2 ( P < 0.001) were analyzed further, representing 143 up-regulated and 152 down-regulated genes, except for unknown transcripts, which were classified into 11 functional categories. The most enriched categories were those of metabolism, signal transduction and cellular transport. Many genes or biological pathways were found to be commonly shared between brace root and lateral or adventitious root development, such as genes participating in cell wall degradation and synthesis, auxin transport and signaling, ethylene signaling, etc. Next, the expression patterns of 20 genes were assessed by quantitative real-time PCR, and the results obtained showed general agreement with the Solexa analysis. Furthermore, a comparison of the brace root transcriptome with that of maize primary root revealed substantial differences in the categories and abundances of expressed transcripts. In conclusion, we first reveal the complex changes in the transcriptome during the early development of maize brace root and provide a comprehensive set of data that are essential for understanding its molecular regulation. [ABSTRACT FROM AUTHOR]

Enzymatic and non-enzymatic antioxidants play important roles in the tolerance of abiotic stress. To increase the resistance of seeds to oxidative stress, At2S3 promoter from Arabidopsis was used to achieve overexpression of the antioxidants in a seed-specific manner. This promoter was shown to be capable of driving the target gene to have a high level of expression in seed-related organs, including siliques, mature seeds, and early seedlings, thus making its molecular farming applications in plants possible. Subsequently, genes encoding Mn-superoxide dismutase ( MSD1), catalase ( CAT1), and homogentisate phytyltransferase ( HPT1, responsible for the first committed reaction in the tocopherol biosynthesis pathway) were overexpressed in Arabidopsis under the control of the At2S3 promoter. Double overexpressers co-expressing two enzymes and triple overexpressers were produced by cross pollination. Mn-SOD and total CAT activities, as well as γ-tocopherol content, significantly increased in the corresponding overproduction lines. Moreover, single MSD1-transgene, double, and triple overexpressers displayed remarkably enhanced oxidative stress tolerance compared to wild type during seed germination and early seedling growth. Interestingly, an increase in the total CAT activity was also observed in the single MSD1-transgenic lines as a result of MSD1 overexpression. Together, the combined increase in Mn-SOD and CAT activities in seeds plays an essential role in the improvement of antioxidant capacity at early developmental stage in Arabidopsis. [ABSTRACT FROM AUTHOR]