Conformational switching in the fungal light sensor Vivid

The Neurospora crassa photoreceptor Vivid tunes blue-light responses and modulates gating of the circadian clock. Crystal structures of dark-state and light-state Vivid reveal a light, oxygen, or voltage Per-Arnt-Sim domain with an unusual N-terminal cap region and a loop insertion that accommodates the flavin cofactor. Photoinduced formation of a cystein-flavin adduct drives flavin protonation to induce an N-terminal conformational change. A cysteine-to-serine substitution remote from the flavin adenine dinucleotide binding site decouples conformational switching from the flavin photocycle and prevents Vivid from sending signals in Neurospora. Key elements of this activation mechanism are conserved by other photosensors such as White Collar-1, ZEITLUPE, ENVOY, and flavin-binding, kelch repeat, F-BOX 1 (FKF1).     

Vision and development in Trichoderma atroviride

Phototropism, the induction of carotenogenesis and reproductive structures, and resetting of the circadian rhythm are controlled by blue light. Trichoderma is used as a photomorphogenetic model due to its ability to conidiate upon exposure to light. In total darkness, T. atroviride grows indefinitely as a mycelium provided that nutrients are not limiting. However, nutrient deprivation and light trigger the conidiation process. A pulse of blue light given to a radially growing colony induc…     

紫外光和蓝光调控查尔酮合成酶基因表达的研究

UV-B（280nm～320nm）、UV-A（320nm～390nm）和蓝光（390nm-500nm）经不同光受体和信号传递途径控制植物发育的各个方面。已知的蓝光／UV-A受体有隐花色素CRY1和CRY2，向光性受体有趋光素。氧化还原过程在隐花色素和趋光素信号转导过程中起重要作用。专一的UV-B光受体尚未被鉴定出，存在许多可能的UV-B信号传递途径．拟南芥查尔酮合成酶（CHS）的紫外光和蓝光转录调控成为研究热点。光受体突变体实验表明存在不同的UV-A／蓝光和UV-B光感知系统调控CHS的表达。拟南芥细胞悬浮培养物实验表明UV-B和CRY1信号传递途径在动力学上和药理学上不同。影响诱导CHS转录的启动子元件和转录因子现已被鉴定出。UV-B、隐花色素和光敏色素信号传递途径之间的相互作用调控CHS表达。UV-B途径与UV-A／蓝光途径的协同相互作用使CHS最大量表达。另外，专一的光敏色素经不同的增强和相巨作用正调控CRY1途径，负调控UV-B途径。     

Photoexcited CRY2 interacts with CIB1 to regulate transcription and floral initiation in Arabidopsis

Cryptochromes (CRY) are photolyase-like blue-light receptors that mediate light responses in plants and animals. How plant cryptochromes act in response to blue light is not well understood. We report here the identification and characterization of the Arabidopsis CIB1 (cryptochrome-interacting basic-helix-loop-helix) protein. CIB1 interacts with CRY2 (cryptochrome 2) in a blue light-specific manner in yeast and Arabidopsis cells, and it acts together with additional CIB1-related proteins to promote CRY2-dependent floral initiation. CIB1 binds to G box (CACGTG) in vitro with a higher affinity than its interaction with other E-box elements (CANNTG). However, CIB1 stimulates FT messenger RNA expression, and it interacts with chromatin DNA of the FT gene that possesses various E-box elements except G box. We propose that the blue light-dependent interaction of cryptochrome(s) with CIB1 and CIB1-related proteins represents an early photoreceptor signaling mechanism in plants.     

A putative role of the xanthophyll, zeaxanthin, in blue light photoreception of corn coleoptiles

Both flavins and carotenoids have some of the attributes expected for a photoreceptor mediating blue light-induced phototropism in plants. Besides the classical photoreceptor candidate, beta-carotene, coleoptiles contain many other carotenoids, including the main components of the xanthophyll cycle, violaxanthin and zeaxanthin. Here, dark-grown coleoptiles accumulated violaxanthin, but lacked zeaxanthin. Coleoptiles devoid of zeaxanthin did not bend in response to a blue light pulse. Coleoptile tips converted violaxanthin into zeaxanthin in the light. Manipulation of coleoptile zeaxanthin content by red light, red light plus darkness, or incubation with the inhibitor of zeaxanthin formation, dithiothreitol, resulted in a blue light-induced bending that was proportional to zeaxanthin content. These data indicate that zeaxanthin may be a blue light photoreceptor in corn coleoptiles.     

JETLAG resets the Drosophila circadian clock by promoting light-induced degradation of TIMELESS

Organisms ranging from bacteria to humans synchronize their internal clocks to daily cycles of light and dark. Photic entrainment of the Drosophila clock is mediated by proteasomal degradation of the clock protein TIMELESS (TIM). We have identified mutations in jetlag-a gene coding for an F-box protein with leucine-rich repeats-that result in reduced light sensitivity of the circadian clock. Mutant flies show rhythmic behavior in constant light, reduced phase shifts in response to light pulses, and reduced light-dependent degradation of TIM. Expression of JET along with the circadian photoreceptor cryptochrome (CRY) in cultured S2R cells confers light-dependent degradation onto TIM, thereby reconstituting the acute response + of the circadian clock to light in a cell culture system. Our results suggest that JET is essential for resetting the clock by transmitting light signals from CRY to TIM.     

光质对大蒜愈伤组织诱导、增殖及器官分化的影响

采用新型半导体光源发光二极管(LED)精量调制光质(红光、蓝光和红蓝组合光),以普通日光灯(白光)为对照,测定大蒜愈伤组织的诱导率及根芽分化率,研究光质对大蒜愈伤组织诱导及植株再生的影响。结果表明,不同光质处理与对照相比均对大蒜愈伤组织的诱导有促进作用,其中以红光出愈时间最短,10 d即有愈伤发生,诱导率最高,达75.78%。红光下愈伤组织增殖速度最快,愈伤组织鲜质量最大,20 d净增量达1.13 g。红光促进大蒜愈伤组织的分化,蓝光和红蓝混合光显著抑制愈伤组织的分化。     

The Neurospora checkpoint kinase 2: a regulatory link between the circadian and cell cycles

The clock gene period-4 (prd-4) in Neurospora was identified by a single allele displaying shortened circadian period and altered temperature compensation. Positional cloning followed by functional tests show that PRD-4 is an ortholog of mammalian checkpoint kinase 2 (Chk2). Expression of prd-4 is regulated by the circadian clock and, reciprocally, PRD-4 physically interacts with the clock component FRQ, promoting its phosphorylation. DNA-damaging agents can reset the clock in a manner that depends on time of day, and this resetting is dependent on PRD-4. Thus, prd-4, the Neurospora Chk2, identifies a molecular link that feeds back conditionally from circadian output to input and the cell cycle.     

光质对狗蔷薇类原球茎发生和植株再生的影响

为探讨光照对狗蔷薇类原球茎的发生和植株再生的影响,采用发光二极管(LED)调制获取不同光谱能量分布的光质配比(纯红光、偏红光(3∶1)、等比光(1∶1)、偏蓝光(1∶3)、纯蓝光),以荧光灯和黑暗作对照,结果表明:偏蓝光条件下狗蔷薇类原球茎的发生率最高,达64%;蓝光、偏红光以及荧光灯下PLBs发生率30%左右,黑暗情况下仅14%。在偏蓝光条件下平均每外植体产生的类原球茎量是其他光质下的2倍。PLBs萌发率在纯红光条件下达到30%,在红蓝混合光下达20%左右,纯蓝光下仅为17%。但在PLBs分化和萌发过程中,含红光条件下的PLBs萌发后更易形成假珠芽,最高达12%,蓝光下仅形成畸形苗。说明不同光质组合对PLBs发育的不同阶段产生不同的影响,偏蓝光有利于狗蔷薇PLBs的发生,红光有利于PLBs的分化和萌发,在含红光的光照下容易诱导出假珠芽。     

Parietal-eye phototransduction components and their potential evolutionary implications

The parietal-eye photoreceptor is unique because it has two antagonistic light signaling pathways in the same cell-a hyperpolarizing pathway maximally sensitive to blue light and a depolarizing pathway maximally sensitive to green light. Here, we report the molecular components of these two pathways. We found two opsins in the same cell: the blue-sensitive pinopsin and a previously unidentified green-sensitive opsin, which we name parietopsin. Signaling components included gustducin-alpha and Galphao, but not rod or cone transducin-alpha. Single-cell recordings demonstrated that Go mediates the depolarizing response. Gustducin-alpha resembles transducin-alpha functionally and likely mediates the hyperpolarizing response. The parietopsin-Go signaling pair provides clues about how rod and cone phototransduction might have evolved.     

Circadian rhythms in Neurospora crassa: oligomycin-resistant mutations affect periodicity

Nuclear mutations conferring resistance to oligomycin, a mitochondrial inhibitor, shorten the period of the circadian conidiation rhythm of Neurospora crassa from the normal 21.5 hours to 18 to 19 hours and slow the linear growth rate by 30 percent. These olir mutations map very close to frq, a locus at which mutations affecting periodicity have been previously obtained. The possibilities are discussed that mitochondria are involved in circadian rhythm generation and that certain period-length mutations affect mitochondrial functions.     

Perception of UV-B by the Arabidopsis UVR8 protein

To optimize their growth and survival, plants perceive and respond to ultraviolet-B (UV-B) radiation. However, neither the molecular identity of the UV-B photoreceptor nor the photoperception mechanism is known. Here we show that dimers of the UVR8 protein perceive UV-B, probably by a tryptophan-based mechanism. Absorption of UV-B induces instant monomerization of the photoreceptor and interaction with COP1, the central regulator of light signaling. Thereby this signaling cascade controlled by UVR8 mediates UV-B photomorphogenic responses securing plant acclimation and thus promotes survival in sunlight.     

LED光源对结球甘蓝(Brassica oleracea var.Capitatal)不定芽再生的影响

为探索不同光源对结球甘蓝(Brassica oleracea var.Capitatal)不定芽再生的影响,采用LED红光、LED黄光、LED蓝光及对照荧光灯光源,选用12-1、12-2、12-3三个结球甘蓝材料进行了研究。结果表明:在LED红、黄、蓝色光源下,外植体愈伤组织的诱导率达100%;在不定芽的诱导中,LED红光的诱导率显著大于LED黄光,与荧光灯没有显著差异,平均诱导率高低依次为:红光>荧光>蓝光>黄光;在继代过程中,从再生系数看,LED红光与LED黄光存在显著差异,与荧光灯存在较明显差异,再生系数高低依次为:红光>蓝光>荧光灯>黄光;在根的诱导中,平均诱导率高低依次为:荧光>红光>蓝光>黄光,培养期间观测发现,LED光源下诱导的根粗壮,须根多,LED红光最明显;但在LED光源培养下有明显的褪绿和瓶壁凝露现象,LED红光下凝露最重;LED光源下先长愈伤组织再长腋芽,叶片变小且易碎,生长势弱,蓝光光源下节间伸长有明显的徒长现象;而荧光灯光源愈伤组织少,腋芽生长正常,没有出现以上现象。     

不同光质LED光照对草菇菌丝生长速度、菌丝分支与生物量的影响

通过探索LED光源在草菇栽培上的精准化应用,为工厂化草菇栽培提供理论依据。以草菇V23为材料,设置LED光质6个处理:对照白光(CK)、红/蓝=1∶1、红/蓝=1∶2、红/蓝=2∶1、单红光、单蓝光,研究不同光质对草菇菌丝生长的影响。结果发现,红光与蓝光的比为1∶1 菌丝长势表现为较强,对其他指标影响不明显。不同LED光源的光质对菌丝生长速度影响很大,从结果可以看出,红蓝光比例为1∶2对菌丝的生长有显著(P<0.05)的作用,并且持续保持领先有促进作用,其次是红蓝光比例为1∶1,并且LED光源的光质对菌丝的影响主要集中在前期,到菌丝后期作用不大。对草菇菌丝生物量的影响最大的是红/蓝光的比例分别为1∶2和1∶1,其分别比CK提高了28.29%和19.97%,呈极显著(P<0.01)差异;同时菌丝分支距离相对较小,分别比CK的菌丝分支距离减少了16.03%和15.13%,整体表现菌丝浓密,且长势相对较强。