SummaryMitochondrial alternative oxidase (AOX) is involved in a large number of plant physiological processes, such as growth, development and stress responses; however, the exact role of AOX in response to drought remains unclear. In our study, we provide solid evidences that the activated AOX capacity positively involved in ethylene‐induced drought tolerance, in tomato (Solanum lycopersicum), accompanied by the changing level of hydrogen peroxide (H2O2) and autophagy. In AOX1a‐RNAi plants, the ethylene‐induced drought tolerance was aggravated and associated with decreasing level of autophagy. The H2O2 level was relatively higher in AOX1a‐RNAi plants, whereas it was lower in AOX1a‐overexpressing (35S‐AOX1a‐OE) plants after 1‐(aminocarbonyl)‐1‐cyclopropanecarboxylic acid (ACC) pretreatment in the 14th day under drought stress. Interestingly, the accumulation of autophagosome was accompanied by the changing level of reactive oxygen species (ROS) in AOX transgenic tomato under drought stress whether or not pretreated with ACC. Pharmacological scavenging of H2O2 accumulation in AOX1a‐RNAi (aox19) stimulated autophagy acceleration under drought stress, and it seems that AOX‐dependent ROS signalling is critical in triggering autophagy. Lower levels of ROS signalling positively induce autophagy activity, whereas higher ROS level would lead to rapid programmed cell death (PCD), especially in ethylene‐mediated drought tolerance. Moreover, ethylene‐induced autophagy during drought stress also can be through ERF5 binding to the promoters of ATG8d and ATG18h. These results demonstrated that AOX plays an essential role in ethylene‐induced drought tolerance and also played important roles in mediating autophagy generation via balancing ROS level.

These authors contributed equally to this work. SUMMARYBrassinosteroids (BRs) play essential roles in modulating plant growth, development and stress responses. Here, involvement of BRs in plant systemic resistance to virus was studied. Treatment of local leaves in Nicotiana benthamiana with BRs induced virus resistance in upper untreated leaves, accompanied by accumulations of H 2 O 2 and NO. Scavenging of H 2 O 2 or NO in upper leaves blocked BR-induced systemic virus resistance. BR-induced systemic H 2 O 2 accumulation was blocked by local pharmacological inhibition of NADPH oxidase or silencing of respiratory burst oxidase homolog gene NbRBOHB, but not by systemic NADPH oxidase inhibition or NbRBOHA silencing. Silencing of the nitrite-dependent nitrate reductase gene NbNR or systemic pharmacological inhibition of NR compromised BR-triggered systemic NO accumulation, while local inhibition of NR, silencing of NbNOA1 and inhibition of NOS had little effect. Moreover, we provide evidence that BR-activated H 2 O 2 is required for NO synthesis. Pharmacological scavenging or genetic inhibiting of H 2 O 2 generation blocked BR-induced systemic NO production, but BR-induced H 2 O 2 production was not sensitive to NO scavengers or silencing of NbNR. Systemically applied sodium nitroprusside rescued BR-induced systemic virus defense in NbRBOHB-silenced plants, but H 2 O 2 did not reverse the effect of NbNR silencing on BR-induced systemic virus resistance. Finally, we demonstrate that the receptor kinase BRI1(BR insensitive 1) is an upstream component in BR-mediated systemic defense signaling, as silencing of NbBRI1 compromised the BR-induced H 2 O 2 and NO production associated with systemic virus resistance. Together, our pharmacological and genetic data suggest the existence of a signaling pathway leading to BR-mediated systemic virus resistance that involves local Respiratory Burst Oxidase Homolog B (RBOHB)-dependent H 2 O 2 production and subsequent systemic NR-dependent NO generation.

Crosstalk between phytohormone pathways is essential in plant growth, development and stress responses. Brassinosteroids (BRs) and ethylene are both pivotal plant growth regulators, and the interaction between these two phytohormones in the tomato response to salt stress is still unclear. Here, we explored the mechanism by which BRs affect ethylene biosynthesis and signaling in tomato seedlings under salt stress. The activity of 1-aminocyclopropane-1-carboxylate synthase (ACS), an ethylene synthesis enzyme, and the ethylene signaling pathway were activated in plants pretreated with BRs. Scavenging of ethylene production or silencing of ethylene signaling components inhibited BR-induced salt tolerance and blocked BR-induced activities of several antioxidant enzymes. Previous studies have reported that BRs can induce plant tolerance to a variety of environmental stimuli by triggering the generation of H2O2 as a signaling molecule. We also found that H2O2 might be involved in the crosstalk between BRs and ethylene in the tomato response to salt stress. Simultaneously, BR-induced ethylene production was partially blocked by pretreated with a reactive oxygen species scavenger or synthesis inhibitor. These results strongly demonstrated that ethylene and H2O2 play important roles in BR-dependent induction of plant salt stress tolerance. Furthermore, we also investigated the relationship between BR signaling and ethylene signaling pathways in plant processes responding to salt stress.

Phenolamides (PAs) are specialized (secondary) metabolites mainly synthesized by BAHD N-acyltransferases. Here, we report metabolic profiling coupled with association and linkage mapping of 11 PAs in rice (Oryza sativa). We identified 22 loci affecting PAs in leaves and 16 loci affecting PAs in seeds. We identified eight BAHD N-acyltransferases located on five chromosomes with diverse specificities, including four aromatic amine N-acyltransferases. We show that genetic variation in PAs is determined, at least in part, by allelic variation in the tissue specificity of expression of the BAHD genes responsible for their biosynthesis. Tryptamine hydroxycinnamoyl transferase 1/2 (Os-THT1/2) and tryptamine benzoyl transferase 1/2 (Os-TBT1/2) were found to be bifunctional tryptamine/tyramine N-acyltransferases. The specificity of Os-THT1 and Os-TBT1 for agmatine involved four tandem arginine residues, which have not been identified as specificity determinants for other plant BAHD transferases, illustrating the versatility of plant BAHD transferases in acquiring new acyl acceptor specificities. With phylogenetic analysis, we identified both divergent and convergent evolution of N-acyltransferases in plants, and we suggest that the BAHD family of tryptamine/tyramine N-acyltransferases evolved conservatively in monocots, especially in Gramineae. Our work demonstrates that omics-assisted gene-to-metabolite analysis provides a useful tool for bulk gene identification and crop genetic improvement.

Plant steroid hormones brassinosteroids (BRs) regulate plant growth and development at many levels. While negative regulatory factors that inhibit development and are counteracted by BRs exist in the root meristem, these factors have not been characterized. The functions of UPB1 transcription factor in BR-regulated root growth have not been established, although its role in regulating root are well documented. Here, we found that BIN2 interacts with and phosphorylates the UPB1 transcription factor consequently promoting UPB1 stability and transcriptional activity. Genetic analysis revealed that UPB1 deficiency could partially recover the short-root phenotype of BR-deficient mutants. Expression of a mutated UPB1 S37AS41A protein lacking a conserved BIN2 phosphorylation sites can rescue shorter root phenotype of bin2-1 mutant. In addition, UPB1 was repressed by BES1 at the transcriptional level. The paclobutrazol-resistant protein family (PRE2/3) interacts with UPB1 and inhibits its transcriptional activity to promote root meristem development, and BIN2-mediated phosphorylation of UPB1 suppresses its interaction with PRE2/3, and subsequently impairing root meristem development. Taken together, our data elucidate a molecular mechanism by which BR promotes root growth via inhibiting BIN2-UPB1 module.

The plant cell wall is the first physical and defensive barrier against pathogens. The plant cell wall usually undergoes dynamic remodeling as an immune response to prevent infection by pathogens. In this review, we summarize advances on relationship between cell wall and immunity in plants. In particular, we outline current progresses regarding the regulation of the cell wall components, including cellulose, hemicellulose, pectin and lignin, on plant disease resistance. We also discuss the impacts of cell wall-derived cellodextrin, oligogalacturonic acid and xyloglucan/xylan oligosaccharides as potent elicitors or signal molecules to trigger plant immune response. We further propose future studies on dissecting the molecular regulation of cell wall on plant immunity, which have potentials in practical application of crop breeding aiming at improvement of plant disease resistance.

No abstract

No abstract