Overexpression of a Kunitz-type trypsin inhibitor (AtKTI1) causes early flowering in Arabidopsis

An early flowering mutant of Arabidopsis, elf32-D was isolated from activation tagging screening. The mutant flowered earlier than wild type under both long day and short day conditions. The mutant phenotype was caused by overexpression of a Kunitz-type trypsin inhibitor gene (AtKTI1). The expression of AtKTI1 was detected in leaves, flowers, siliques and roots. In the vegetative state, no change of flowering integrator gene expression was observed for AtKTI1 overexpressing plants. In contrast, at the reproductive stage, its overexpression resulted in the down-regulation of FLC, a strong floral repressor which integrates the autonomous and vernalization pathways and also the up-regulation of FT and AP1, which are downstream floral integrator genes. It is probable that the AtKTI1 overexpression inhibits components of the flowering signaling pathway upstream of FLC, eventually regulating expression of FLC, or causing perturbations in plant metabolism and thus indirectly affecting flowering.     

SHB1 plays dual roles in photoperiodic and autonomous flowering

Flowering was initiated by the integration of environmental signals such as day-length with the internal development status in Arabidopsis, a facultative long-day plant. The photoperiodic flowering involves two key components, CONSTANS and FT, whereas the autonomous flowering is operated through a central quantitative floral repressor, FLC, and several other genes that act upstream of FLC. SOC1 acts downstream to integrate the flowering signals from the two pathways. Here, we report that SHB1 plays dual roles in both photoperiodic and autonomous flowering. shb1-D, a gain-of-function mutant, flowered early and shb1, a loss-of-function allele, flowered late under both long days and short days. The shb1-D mutation activated the expression of CO, FT, and SOC1 under both long and short days, and however, the co-2 mutation attenuated the shb1-D activated expression of FT and SOC1 only under long days but not short days. The shb1-D or shb1 mutations also reduced and increased, respectively, the expression of FLC under both long and short days. Transgenic remedy of FLC to wide-type level in shb1-D background also reverted shb1-D flowering and FT or SOC1 expression to wild type mostly under short days. Furthermore, the shb1-D suppression on FLC expression is likely operated through LD as ld-3 blocked this suppression and SHB1 appears to act upstream of LD. In summary, SHB1 represents signaling steps that regulate CO expression in leaves and LD or FLC expression in either leaves or shoot apical meristem, contributing to a threshold expression of SOC1 in shoot apical meristem for floral initiation.     

大豆开花基因GmCO和GmFT的克隆及表达

为了研究大豆光周期反应是否受开花基因CO(CONSTANS)和FT(FLOWERING LOCUS T)调控,采用同源序列法从大豆中分离了CO和FT的同源物GmCO和GmFT.GmCO和GmFT分别编码151和109个氨基酸,与水稻和拟南芥中相关蛋白的氨基酸序列同源性达到70%以上.通过RT-PCR分析GmCO和GmFT在短日照(short daylength,SD)、自然光照(natural light,NL)和长日照(long daylength,LD)处理大豆不同发育阶段叶片中的表达发现,GmCO在LD处理大豆早期发育的叶片中高丰度表达,GmFT在SD和NL处理大豆开花时期的叶片中高丰度表达.上述结果表明,GmCO和GmFT的表达与大豆开花时间及光照长度密切相关,且GmCO抑制GmFT的表达.     

RNF4 interacts with both SUMO and nucleosomes to promote the DNA damage response

The post‐translational modification of DNA repair and checkpoint proteins by ubiquitin and small ubiquitin‐like modifier (SUMO) critically orchestrates the DNA damage response (DDR). The ubiquitin ligase RNF4 integrates signaling by SUMO and ubiquitin, through its selective recognition and ubiquitination of SUMO‐modified proteins. Here, we define a key new determinant for target discrimination by RNF4, in addition to interaction with SUMO. We identify a nucleosome‐targeting motif within the RNF4 RING domain that can bind DNA and thereby enables RNF4 to selectively ubiquitinate nucleosomal histones. Furthermore, RNF4 nucleosome‐targeting is crucially required for the repair of TRF2‐depleted dysfunctional telomeres by 53BP1‐mediated non‐homologous end joining.     

蛋白质多聚SUMO化修饰及其功能

泛素（ubiquitin, Ub）是一类高度保守的小蛋白, 可与靶蛋白的赖氨酸残基共价连接, 形成多聚泛素链行使功能. 类似于泛素化修饰过程, 小泛素相关修饰物(small ubiquitin related modifier, SUMO）也可以共价修饰靶蛋白的赖氨酸残基, 从而影响靶蛋白的定位、稳定性以及蛋白间的相互作用, 发挥重要的生理功能. 尽管在多数情况下, 靶蛋白发生的是单SUMO化修饰, 但最近研究发现,SUMO依赖自身的赖氨酸也可以形成多聚链. 与单SUMO化修饰不同的是, 多聚SUMO化修饰的靶蛋白可以进一步被泛素化修饰, 进而诱导靶蛋白的降解. 这是一种新的、特殊的化学修饰形式, 弄清它的生理功能,对于了解细胞的生长、分化以及凋亡等生理过程将具有重要的意义. 本文将就此方面的最新研究进展做一综述.     

Florigen goes molecular: Seventy years of the hormonal theory of flowering regulation

As early as in 1936, the comprehensive studies of flowering led M.Kh. Chailakhyan to the concept of florigen, a hormonal floral stimulus, and let him establish several characteristics of this stimulus. These studies set up for many years the main avenues for research into the processes that control plant flowering, and the notion of florigen became universally accepted by scientists worldwide. The present-day evidence of genetic control of plant flowering supports the idea that florigen participates in floral signal transduction. The recent study of arabidopsis plants led the authors to conclusion that the immediate products of the gene FLOWERING LOCUS I, its mRNA and/or protein, move from an induced leaf into the shoot apex and evoke flowering therein.     

Optical Rotatory Dispersion and Circular Dichroism of the Carboxyl Chromophore in Gibbane-10-carboxylic Acids with an Aromatic A Ring,and Their Application to the Stereochemistry of the B Ring of Gibberellins and Their Derivatives

CD and ORD of twelve gibbane-10-carboxylic acid compounds with an aromatic A ring together with two related compounds were measured. The sign of the Cotton effect was found to be positive (negative) when the configuration of the C–10 carboxyl is β (α). The ORD also provided information to determine the configuration at C–4b. The C–10 carboxyl gave a stronger magnitude and redshift of the peak in a cis relation with 4b–H compared with that in a trans relation.     

VASCULAR PLANT ONE-ZINC FINGER1 and VOZ2 repress the FLOWERING LOCUS C clade members to control flowering time in Arabidopsis

Floral transition is regulated by environmental and endogenous signals. Previously, we identified VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1) and VOZ2 as phytochrome B-interacting factors. VOZ1 and VOZ2 redundantly promote flowering and have pivotal roles in the downregulation of FLOWERING LOCUS C (FLC), a central repressor of flowering in Arabidopsis. Here, we showed that the late-flowering phenotypes of the voz1 voz2 mutant were suppressed by vernalization in the Columbia and FRIGIDA (FRI)-containing accessions, which indicates that the late-flowering phenotype of voz1 voz2 mutants was caused by upregulation of FLC. We also showed that the other FLC clade members, MADS AFFECTING FLOWERING (MAF) genes, were also a downstream target of VOZ1 and VOZ2 as their expression levels were also increased in the voz1 voz2 mutant. Our results suggest that the FLC clade genes integrate signals from VOZ1/VOZ2 and vernalization to regulate flowering.     

In Vitro Studies Reveal a Sequential Mode of Chain Processing by the Yeast SUMO (Small Ubiquitin-related Modifier)-specific Protease Ulp2

Sumoylation is a post-translational modification essential in most eukaryotes that regulates stability, localization, activity, or interaction of a multitude of proteins. It is a reversible process wherein counteracting ligases and proteases, respectively, mediate the conjugation and deconjugation of SUMO molecules to/from target proteins. Apart from attachment of single SUMO moieties to targets, formation of poly-SUMO chains occurs by the attachment of additional SUMO molecules to lysine residues in the N-terminal extensions of SUMO. In Saccharomyces cerevisiae there are apparently only two SUMO(Smt3)-specific proteases: Ulp1 and Ulp2. Ulp2 has been shown to be important for the control of poly-SUMO conjugates in cells and to dismantle SUMO chains in vitro, but the mechanism by which it acts remains to be elucidated. Applying an in vitro approach, we found that Ulp2 acts sequentially rather than stochastically, processing substrate-linked poly-SUMO chains from their distal ends down to two linked SUMO moieties. Furthermore, three linked SUMO units turned out to be the minimum length of a substrate-linked chain required for efficient binding to and processing by Ulp2. Our data suggest that Ulp2 disassembles SUMO chains by removing one SUMO moiety at a time from their ends (exo mechanism). Apparently, Ulp2 recognizes surfaces at or near the N terminus of the distal SUMO moiety, as attachments to this end significantly reduce cleavage efficiency. Our studies suggest that Ulp2 controls the dynamic range of SUMO chain lengths by trimming them from the distal ends.