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Summary: Stomatal density (SD) is closely related to crop drought resistance. Understanding the genetic basis for natural variation in SD may facilitate efforts to improve water‐use efficiency. Here, we report a genome‐wide association study for SD in maize seedlings, which identified 18 genetic variants that could be resolved to seven candidate genes. A 3‐bp insertion variant (InDel1089) in the last exon of Zea mays (Zm) IRX15A (Irregular xylem 15A) had the most significant association with SD and modulated the translation of ZmIRX15A mRNA by affecting its secondary structure. Dysfunction of ZmIRX15A increased SD, leading to an increase in the transpiration rate and CO2 assimilation efficiency. ZmIRX15A encodes a xylan deposition enzyme and its disruption significantly decreased xylan abundance in secondary cell wall composition. Transcriptome analysis revealed a substantial alteration of the expression of genes involved in stomatal complex morphogenesis and drought response in the loss‐of‐function of ZmIRX15A mutant. Overall, our study provides important genetic insights into the natural variation of leaf SD in maize, and the identified loci or genes can serve as direct targets for enhancing drought resistance in molecular‐assisted maize breeding. [ABSTRACT FROM AUTHOR]

Water uptake is crucial for crop growth and development and drought stress tolerance. The water channel aquaporins (AQP) play important roles in plant water uptake. Here, we discovered that a jasmonic acid analog, coronatine (COR), enhanced maize (Zea mays) root water uptake capacity under artificial water deficiency conditions. COR treatment induced the expression of the AQP gene Plasma membrane intrinsic protein 2;5 (ZmPIP2;5). In vivo and in vitro experiments indicated that COR also directly acts on ZmPIP2;5 to improve water uptake in maize and Xenopus oocytes. The leaf water potential and hydraulic conductivity of roots growing under hyperosmotic conditions were higher in ZmPIP2;5‐overexpression lines and lower in the zmpip2;5 knockout mutant, compared to wild‐type plants. Based on a comparison between ZmPIP2;5 and other PIP2s, we predicted that COR may bind to the functional site in loop E of ZmPIP2;5. We confirmed this prediction by surface plasmon resonance technology and a microscale thermophoresis assay, and showed that deleting the binding motif greatly reduced COR binding. We identified the N241 residue as the COR‐specific binding site, which may activate the channel of the AQP tetramer and increase water transport activity, which may facilitate water uptake under hyperosmotic stress. [ABSTRACT FROM AUTHOR]

Brown carbon (BrC) has been recognized as an important contributor to global warming due to its absorption of solar radiation with strong wavelength dependence. While early studies mostly consider biomass burning as a major emission source, a few recent studies have suggested coal combustion and vehicle exhaust as important contributors to BrC emissions. Considering dominant coal consumption, large residential biofuel usage, and the increasing number of vehicles, BrC pollution could result in remarkable regional climate effects in China. This study gives an overview of sources, chemical composition and absorption properties of BrC, focusing on BrC categorization and its absorption measurement techniques. The basic pollution features of BrC in China, including surface concentrations, column burden, sources and associated absorbing properties are then summarized and compared to other countries. BrC emissions as well as its optical emission at 365 nm from the primary sources in China are also summarized to provide a more straightforward understanding of the light‐absorbing properties of BrC in China. With a detailed comparison of existing publications, the study gives deeper insight into the uncertainties in BrC measurements and will improve the understanding of the climate effect of BrC. The review also recommends key research areas for further investigation of BrC in the future. Plain Language Summary: Brown carbon (BrC) is a collection of organic compounds with brownish color. It has been identified as an important component of atmospheric absorbing aerosols and plays a substantial role in climate change. However, there is still a great challenge to precisely evaluate the climate effect of BrC. The difficulties stem mainly from the lack of the estimates of BrC emissions as well as the high variability of its light absorption ability. This review summarizes BrC sources, absorption ability, and pollution levels in China. The large energy consumption in China with dominant coal combustion and substantial residential biomass burning makes China a potentially large BrC emission source region and explains the observed relatively high BrC pollution level. The contributions of fossil fuel combustion to BrC emission and light absorption are comparable to those from biomass burning in China, although with large uncertainties. During the last decade, BrC emission from biomass burning and coal combustion decreases in China due to the change in energy structure associated with the implementation of emission control measures. To better address the climate impacts of BrC, further efforts devoted to the measurements of BrC, in particular its absorption ability from different sources are in urgent need. Key Points: BrC concentrations and absorption in China are much higher than in the USA, but similar to IndiaEmission and absorbing ability of BrC from fossil fuel combustion are comparable to or even larger than those from biomass burningDuring the last decade, BrC emission from biomass burning and coal combustion decreases in China [ABSTRACT FROM AUTHOR]