Panpan Li

Acanthoscelides obtectus (Say, 1831) threatens bean production and storage. We assessed its climatic suitability in China using an optimized maximum entropy (MaxEnt) model with seven bioclimatic variables. Final fitting used 342 spatially thinned occurrences and 10,000 background points sampled in proportion to cell area. Projections covered three global climate models, three Shared Socioeconomic Pathways (SSPs), and three future periods. Five-fold outer spatial validation yielded an area under the receiver operating characteristic curve of 0.78 ± 0.05 and a continuous Boyce index of 0.87 ± 0.10. Temperature annual range, maximum temperature of the warmest month, and mean temperature of the wettest quarter had the highest normalized permutation importance. Baseline projections (1970–2000) identified 3.02 million km² of potentially suitable areas, mainly in southwestern and southern China and along the eastern coast. Under the primary M500 calibration, all nine ensembles showed total-area declines, high-suitability losses and westward centroid shifts. For late-century SSP5-8.5, the primary ensemble projected a 1.41% total-area decline and a 93.92% high-suitability loss (s ≥ 0.75). Total-area change reversed direction across backgrounds, GCM compositions and bootstrap fits, whereas westward shifts persisted. Centroid-shift direction was thus more consistent than area-change direction across these comparisons, informing climate-based surveillance.

Plant membrane sterol composition has been reported to affect growth and gravitropism via polar auxin transport and auxin signaling. However, as to whether sterols influence auxin biosynthesis has received little attention. Here, by using the sterol biosynthesis mutant cyclopropylsterol isomerase1-1 (cpi1-1) and sterol application, we reveal that cycloeucalenol, a CPI1 substrate, and sitosterol, an end-product of sterol biosynthesis, antagonistically affect auxin biosynthesis. The short root phenotype of cpi1-1 was associated with a markedly enhanced auxin response in the root tip. Both were neither suppressed by mutations in polar auxin transport (PAT) proteins nor by treatment with a PAT inhibitor and responded to an auxin signaling inhibitor. However, expression of several auxin biosynthesis genes TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 (TAA1) was upregulated in cpi1-1. Functionally, TAA1 mutation reduced the auxin response in cpi1-1 and partially rescued its short root phenotype. In support of this genetic evidence, application of cycloeucalenol upregulated expression of the auxin responsive reporter DR5:GUS (β-glucuronidase) and of several auxin biosynthesis genes, while sitosterol repressed their expression. Hence, our combined genetic, pharmacological, and sterol application studies reveal a hitherto unexplored sterol-dependent modulation of auxin biosynthesis during Arabidopsis root elongation.

Sterols are essential molecules for multiple biological processes, including embryogenesis, cell elongation, and endocytosis. The plant sterol biosynthetic pathway is unique in the involvement of two distinct sterol C-4-methyl oxidase (SMO) families, SMO1 and SMO2, which contain three and two isoforms, respectively, and are involved in sequential removal of the two methyl groups at C-4. In this study, we characterized the biological functions of members of the SMO2 gene family. SMO2-1 was strongly expressed in most tissues during Arabidopsis development, whereas SMO2-2 showed a more specific expression pattern. Although single smo2 mutants displayed no obvious phenotype, the smo2-1 smo2-2 double mutant was embryonic lethal, and the smo2-1 smo2-2/+ mutant was dwarf, whereas the smo2-1/+ smo2-2 mutant exhibited a moderate phenotype. The phenotypes of the smo2 mutants resembled those of auxin-defective mutants. Indeed, the expression of DR5rev:GFP, an auxin-responsive reporter, was reduced and abnormal in smo2-1 smo2-2 embryos. Furthermore, the expression and subcellular localization of the PIN1 auxin efflux facilitator were also altered. Consistent with these observations, either the exogenous application of auxin or endogenous auxin overproduction (YUCCA9 overexpression, YUC9 OE) partially rescued the smo2-1 smo2-2 embryonic lethality. Surprisingly, the dwarf phenotype of the smo2-1 smo2-2/+ was completely rescued by YUC9 OE. GC-MS analysis revealed a substantial accumulation of 4α-methylsterols, substrates of SMO2, in smo2 heterozygous double mutants. Together, our data suggest that SMO2s are important for correct sterol composition and function partially through effects on auxin accumulation, auxin response and PIN1 expression to regulate Arabidopsis embryogenesis and postembryonic development.