Cotyledons facilitate the adaptation of early-maturing soybean varieties to high-latitude long-day environments.

Soybean (Glycine max), a typical short-day plant (SDP) domesticated in temperate regions, has expanded to high latitudes where daylengths are long from soybean emergence to bloom, but rapidly decrease from seed filling to maturity. Cotyledons are well known as the major storage organs in seeds, but it is unclear whether developing cotyledons store flowering substances at filling stage in SD for upcoming seedlings, or instead respond to photoperiod for floral induction after emergence of matured seeds in long-day (LD). Here, we report that cotyledons accelerate flowering of early-maturing varieties not resulting from stored floral stimuli but by perceiving photoperiod after emergence. We found that light signal is indispensable to activate cotyledons for floral induction, and flowering promoting gene GmFT2a is required for cotyledon-dependent floral induction via upregulation of floral identity gene GmAP1. Interestingly, cotyledons are competent to support the entire life cycle of a cotyledon-only plant to produce seeds, underlying a new photoperiod study system in soybean and other dicots. Taken together, these results demonstrate a substantial role for cotyledons in flowering process, whereby we propose a 'cotyledon-based self-reliance' model highlighting floral induction from emergence as a key ecological adaptation for rapid flowering of SDPs grown in LD environments at high latitudes.

Exploiting the trifluoroethyl group as a precatalyst ligand in nickel-catalyzed Suzuki-type alkylations.

We report herein the exploitment of the partially fluorinated trifluoroethyl as precatalyst ligands in nickel-catalyzed Suzuki-type alkylation and fluoroalkylation coupling reactions. Compared with the [L n NiII(aryl)(X)] precatalysts, the unique characters of bis-trifluoroethyl ligands imparted precatalyst [(bipy)Ni(CH2CF3)2] with bench-top stability, good solubilities in organic media and interesting catalytic activities. Preliminary mechanistic studies reveal that an eliminative extrusion of a vinylidene difluoride (VDF, CH2[double bond, length as m-dash]CF2) mask from [(bipy)Ni(CH2CF3)2] is a critical step for the initiation of a catalytic reaction.

The catalytic roles of P185 and T188 and substrate-binding loop flexibility in 3α-hydroxysteroid dehydrogenase/carbonyl reductase from Comamonas testosteroni.

3α-Hydroxysteroid dehydrogenase/carbonyl reductase from Comamonas testosteroni reversibly catalyzes the oxidation of androsterone with NAD(+) to form androstanedione and NADH. Structurally the substrate-binding loop of the residues, T188-K208, is unresolved, while binding with NAD(+) causes the appearance of T188-P191 in the binary complex. This study determines the functional roles of the flexible substrate-binding loop in conformational changes and enzyme catalysis. A stopped-flow study reveals that the rate-limiting step in the reaction is the release of the NADH. The mutation at P185 in the hinge region and T188 in the loop causes a significant increase in the Kd value for NADH by fluorescence titration. A kinetic study of the mutants of P185A, P185G, T188A and T188S shows an increase in k(cat), K(androsterone) and K(iNAD) and equal primary isotope effects of (D)V and (D) (V/K). Therefore, these mutants increase the dissociation of the nucleotide cofactor, thereby increasing the rate of release of the product and producing the rate-limiting step in the hydride transfer. Simulated molecular modeling gives results that are consistent with the conformational change in the substrate-binding loop after NAD(+) binding. These results indicate that P185, T188 and the flexible substrate-binding loop are involved in binding with the nucleotide cofactor and with androsterone and are also involved in catalysis.