Autophagy receptor ZmNBR1 promotes the autophagic degradation of ZmBRI1a and enhances drought tolerance in maize.

Drought stress is a crucial environmental factor that limits plant growth, development, and productivity. Autophagy of misfolded proteins can help alleviate the damage caused in plants experiencing drought. However, the mechanism of autophagy-mediated drought tolerance in plants remains largely unknown. Here, we cloned the gene for a maize (Zea mays) selective autophagy receptor, NEXT TO BRCA1 GENE 1 (ZmNBR1), and identified its role in the response to drought stress. We observed that drought stress increased the accumulation of autophagosomes. RNA sequencing and reverse transcription-quantitative polymerase chain reaction showed that ZmNBR1 is markedly induced by drought stress. ZmNBR1 overexpression enhanced drought tolerance, while its knockdown reduced drought tolerance in maize. Our results established that ZmNBR1 mediates the increase in autophagosomes and autophagic activity under drought stress. ZmNBR1 also affects the expression of genes related to autophagy under drought stress. Moreover, we determined that BRASSINOSTEROID INSENSITIVE 1A (ZmBRI1a), a brassinosteroid receptor of the BRI1-like family, interacts with ZmNBR1. Phenotype analysis showed that ZmBRI1a negatively regulates drought tolerance in maize, and genetic analysis indicated that ZmNBR1 acts upstream of ZmBRI1a in regulating drought tolerance. Furthermore, ZmNBR1 facilitates the autophagic degradation of ZmBRI1a under drought stress. Taken together, our results reveal that ZmNBR1 regulates the expression of autophagy-related genes, thereby increasing autophagic activity and promoting the autophagic degradation of ZmBRI1a under drought stress, thus enhancing drought tolerance in maize. These findings provide new insights into the autophagy degradation of brassinosteroid signaling components by the autophagy receptor NBR1 under drought stress.

Unusual ent-Labdane Diterpenoid Dimers and their Selective Activation of TRPV Channels.

Five unusual dimers of ent-labdane diterpenoids (1-5) were isolated and identified from Andrographis paniculata, a famous medicinal plant. Bisandrographolide E (1) represents the first example of a labdane dimer possessing an unprecedent tricyclic system that comprised a spiroketal moiety fused with a ketal-γ-lactone unit in its skeleton. Its biosynthetically related intermediates, all four stereoisomers at C-12 and C-15', bisandrographolides F (2, a new compound) and A-C (3-5), were obtained at the same time. The steric configurations of the newly formed asymmetric carbons in 1-5 were first solved by single-crystal X-ray diffraction of the diacetone derivatives of 2-4 and ECD and NMR calculations of 1. More importantly, bisandrographolides 1-5, with different chemical structures or absolute configurations at C-12 and C-15', selectively activated different TRPV1-4 channels and protected cardiomyocytes from hypoxia-reoxygenation injury. Among them, 5 with 12R/15'S configuration activated TRPV1 most effectively and displayed the best cardiomyocyte protection.

Pectin methylesterase 31 is transcriptionally repressed by ABI5 to negatively regulate ABA-mediated inhibition of seed germination.

Pectin methylesterase (PME), a family of enzymes that catalyze the demethylation of pectin, influences seed germination. Phytohormone abscisic acid (ABA) inhibits seed germination. However, little is known about the function of PMEs in response to ABA-mediated seed germination. In this study, we found the role of PME31 in response to ABA-mediated inhibition of seed germination. The expression of PME31 is prominent in the embryo and is repressed by ABA treatment. Phenotype analysis showed that disruption of PME31 increases ABA-mediated inhibition of seed germination, whereas overexpression of PME31 attenuates this effect. Further study found that ABI5, an ABA signaling bZIP transcription factor, is identified as an upstream regulator of PME31. Genetic analysis showed that PME31 functions downstream of ABI5 in ABA-mediated seed germination. Detailed studies showed that ABI5 directly binds to the PME31 promoter and inhibits its expression. In the plants, PME31 expression is reduced by ABI5 in ABA-mediated seed germination. Taken together, PME31 is transcriptionally inhibited by ABI5 and negatively regulates ABA-mediated seed germination inhibition. These findings shed new light on the mechanisms of PMEs in response to ABA-mediated seed germination.

Withanolides and aromatic glycosides isolated from Nicandra physaloides and their anti-inflammatory activity.

Two new withanolides (1-2) together with five known ones (3-7), and three known aromatic glycosides (8-10) were isolated from the dried stems and leaves of Nicandra physaloides, an edible and medicinal plant. Their structures were identified by extensive spectroscopic analyses or comparison with literature data. The absolute configuration of 2 was assigned via X-ray crystallography. Compound 1 with a spiroketal moiety is relatively unusual in withanolides. Aromatic glycosides (8-10) showed potent inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages, with IC50 values from 4.69 to 16.12 µM.