In eukaryotic cells, the unfolded protein response (UPR) pathway plays a crucial role in cellular homeostasis of the endoplasmic reticulum (ER) during exposure to diverse environmental conditions that cause ER stress. Here we report that the human fungal pathogen Cryptococcus neoformans has evolved a unique UPR pathway composed of an evolutionarily conserved Ire1 protein kinase and a novel bZIP transcription factor encoded by HXL1 (HAC1 and XBP1-Like gene 1). C. neoformans HXL1 encodes a protein lacking sequence homology to any known fungal or mammalian Hac1/Xbp1 protein yet undergoes the UPR-induced unconventional splicing in an Ire1-dependent manner upon exposure to various stresses. The structural organization of HXL1 and its unconventional splicing is widely conserved in C. neoformans strains of divergent serotypes. Notably, both C. neoformans ire1 and hxl1 mutants exhibited extreme growth defects at 37°C and hypersensitivity to ER stress and cell wall destabilization. All of the growth defects of the ire1 mutant were suppressed by the spliced active form of Hxl1, supporting that HXL1 mRNA is a downstream target of Ire1. Interestingly, however, the ire1 and hxl1 mutants showed differences in thermosensitivity, expression patterns for a subset of genes, and capsule synthesis, indicating that Ire1 has both Hxl1-dependent and -independent functions in C. neoformans. Finally, Ire1 and Hxl1 were shown to be critical for virulence of C. neoformans, suggesting UPR signaling as a novel antifungal therapeutic target.

RAM (regulation of Ace2p transcription factor and polarized morphogenesis) is a conserved signaling network that regulates polarized morphogenesis in yeast, worms, flies, and humans. To investigate the role of the RAM network in cell polarity and hyphal morphogenesis of Candida albicans, each of the C. albicans RAM genes (CaCBK1, CaMOB2, CaKIC1, CaPAG1, CaHYM1, and CaSOG2) was deleted. All C. albicans RAM mutants exhibited hypersensitivity to cell-wall- or membrane-perturbing agents, exhibiting cell-separation defects, a multinucleate phenotype and loss of cell polarity. Yeast two-hybrid and in vivo functional analyses of CaCbk1p and its activator, CaMob2p, the key factors in the RAM network, demonstrated that the direct interaction between the SMA domain of CaCbk1p and the Mob1/phocein domain of CaMob2p was necessary for hyphal growth of C. albicans. Genome-wide transcription profiling of a Camob2 mutant suggested that the RAM network played a role in serum- and antifungal azoles-induced activation of ergosterol biosynthesis genes, especially those involved in the late steps of ergosterol biosynthesis, and might be associated, at least indirectly, with the Tup1p-Nrg1p pathway. Collectively, these results demonstrate that the RAM network is critically required for hyphal growth as well as normal vegetative growth in C. albicans.

Organic–inorganic hybrid nanoflowers, a newly developed class of flower-like hybrid nanoparticles, have received much attention due to their simple synthesis, high efficiency, and enzyme stabilizing ability. This article covers, in detail, the types, structural features, mechanism of formation, and bio-related applications of hybrid nanoflowers. The five major types of hybrid nanoflowers are discussed, i.e., copper–protein, calcium–protein, and manganese–protein hybrid nanoflowers, copper–DNA hybrid nanoflowers, and capsular hybrid nanoflowers. The structural features of these nanoflowers, such as size, shape, and protein ratio generally determine their applications. Thus, the specific characteristics of hybrid nanoflowers are summarized in this review. The interfacial mechanism of nanoflower formation is examined in three steps: first, combination of metal ion and organic matter; second, formation of petals; third, growth of nanoflowers. The explanations provided herein can be utilized in the development of innovative approaches for the synthesis of hybrid nanoflowers for prospective development of a plethora of hybrid nanoflowers. The future prospects of hybrid nanoflowers in the biotechnology industry, medicine, sensing, and catalysis are also discussed.

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