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Leaf senescence is important for crop yield as delaying it can increase the average yield. In this study, population genetics and transcriptomic profiling were combined to dissect its genetic basis in maize. To do this, the progenies of an elite maize hybrid Jidan27 and its parental lines Si-287 (early senescence) and Si-144 (stay-green), as well as 173 maize inbred lines were used. We identified two novel loci and their candidate genes, Stg3 (ZmATG18b) and Stg7 (ZmGH3.8), which are predicted to be members of autophagy and auxin pathways, respectively. Genomic variations in the promoter regions of these two genes were detected, and four allelic combinations existed in the examined maize inbred lines. The Stg3 Si-144/ Stg7 Si-144 allelic combination with lower ZmATG18b expression and higher ZmGH3.8 expression could distinctively delay leaf senescence, increase ear weight and the improved hybrid of NIL- Stg3Si-144 / Stg7Si-144 × Si-144 significantly reduced ear weight loss under drought stress, while opposite effects were observed in the Stg3 Si-287/ Stg7 Si-287 combination with a higher ZmATG18b expression and lower ZmGH3.8 expression. Thus, we identify a potential interaction between autophagy and auxin which could modulate the timing of maize leaf senescence. [ABSTRACT FROM AUTHOR]

Arabidopsis thaliana respiratory burst oxidase homolog D (RbohD) functions as an essential regulator of reactive oxygen species (ROS). However, our understanding of the regulation of RbohD remains limited. By variable-angle total internal reflection fluorescence microscopy, we demonstrate that green fluorescent protein (GFP)-RbohD organizes into dynamic spots at the plasma membrane. These RbohD spots have heterogeneous diffusion coefficients and oligomerization states, as measured by photobleaching techniques. Stimulation with ionomycin and calyculin A, which activate the ROS -producing enzymatic activity of RbohD, increases the diffusion and oligomerization of RbohD. Abscisic acid and flg22 treatments also increase the diffusion coefficient and clustering of GFP-RbohD. Single-particle analysis in clathrin heavy chain2 mutants and a Flotillin1 artificial microRNA line demonstrated that clathrin- and microdomain-dependent endocytic pathways cooperatively regulate RbohD dynamics. Under salt stress, GFP-RbohD assembles into clusters and then internalizes into the cytoplasm. Dual-color fluorescence cross-correlation spectroscopy analysis further showed that salt stress stimulates RbohD endocytosis via membrane microdomains. We demonstrate that microdomain-associated RbohD spots diffuse at the membrane with high heterogeneity, and these dynamics closely relate to RbohD activity. Our results provide insight into the regulation of RbohD activity by clustering and endocytosis, which facilitate the activation of redox signaling pathways. [ABSTRACT FROM AUTHOR]

Under blue light (BL) illumination, Arabidopsis thaliana roots grow away from the light source, showing a negative phototropic response. However, the mechanism of root phototropism is still unclear. Using a noninvasive microelectrode system, we showed that the BL sensor phototropin1 (phot1), the signal transducer NONPHOTOTROPIC HYPOCOTYL3 (NPH3), and the auxin efflux transporter PIN2 were essential for BL-induced auxin flux in the root apex transition zone. We also found that PIN2-green fluorescent protein (GFP) localized to vacuole-like compartments (VLCs) in dark-grown root epidermal and cortical cells, and phot1/NPH3 mediated a BL-initiated pathway that caused PIN2 redistribution to the plasma membrane. When dark-grown roots were exposed to brefeldin A (BFA), PIN2-GFP remained in VLCs in darkness, and BL caused PIN2-GFP disappearance from VLCs and induced PIN2-GFP-FM4-64 colocalization within enlarged compartments. In the nph3 mutant, both dark and BL BFA treatments caused the disappearance of PIN2-GFP from VLCs. However, in the phot1 mutant, PIN2-GFP remained within VLCs under both dark and BL BFA treatments, suggesting that phot1 and NPH3 play different roles in PIN2 localization. In conclusion, BL-induced root phototropism is based on the phot1/NPH3 signaling pathway, which stimulates the shootward auxin flux by modifying the subcellular targeting of PIN2 in the root apex transition zone. [ABSTRACT FROM AUTHOR]