Fatty acid-binding proteins (FABPs) are a family of lipid chaperones, which contribute to systemic metabolic regulation through diverse lipid signalings.  In this study, a midgut-specific FABP gene (Slfabp2) was cloned from Spodoptera litura.  RT-PCR and Western blot analysis indicated that RNA and protein levels of SlFABP2 gradually increased and reached a peak at the prepupal stage and maintained a high level during the pupal stage.  The expression of SlFABP2 protein was induced by starvation treatment.  In vitro binding assay revealed that the recombinant SlFABP2 had high affinities of binding long-chain fatty acids, such as palmitic acid, arachidonate and oleic acid.  The results suggest that SlFABP2 may have a unique function that transports intracellular fatty acids and can regulate the metabolism of lipids in metamorphosis.  This work provides experimental clues for understanding the potential function of SlFABP2 in fatty acid metabolism in S. litura.

 

Soil microbes play essential roles in the biogeochemical processes of organic carbon and nutrient cycling.  Many studies have reported various short-term effects of fertilization on soil microbes.  However, less is known about the effects of long-term fertilization regimes on the rhizosphere.  Therefore, the objective of this study was to explore how the soil microbial communities in the rhizosphere respond to different long-term fertilization strategies.  Based on a 21-year field treatment experiment in Guizhou, China, we extracted phospholipid fatty acids (PLFAs) to determine the microbial community structure in both the non-rhizosphere (NR) and rhizosphere (R).  Six treatments were included: no fertilizer (CK), mineral nitrogen fertilizer (N), N with potassium (NK), phosphorus with K (PK), NPK, and NPK combined with manure (MNPK).  The results showed that total PLFAs under unbalanced mineral fertilization (N, NK and PK) were decreased by 45% on average in the NR compared with CK, whereas MNPK increased fungi and G–bacteria abundance significantly in both the NR (by 33 and 23%) and R (by 15 and 20%), respectively.  In addition, all microbial groups in the R under these treatments (N, NK and PK) were significantly increased relative to those in the NR, except for the ratio of F/B and G+/G–, which might be due to the high nutrient availability in the R.  Soil pH and SOC significantly regulated the soil microbial community and structure, explaining 51 and 20% of the variation in the NR, respectively.  However, the rhizosphere microbial community structure was only significantly affected by soil pH (31%).  We concluded that the soil microbial community in the NR was more strongly affected by long-term fertilization than that in the R due to the rhizosphere effect in the agricultural ecosystem.  Rhizosphere nutrient conditions and buffering capacity could help microbial communities resist the change from the long-term fertilization.

Asparagine is an efficient nitrogen transport and storage carrier.  Asparagine synthesis occurs by the amination of aspartate which is catalyzed by asparagine synthetase (ASN) in plants.  Complete genome-wide analysis and classifications of the ASN gene family have recently been reported in different plants.  However, systematic analysis and expression profiles of these genes have not been performed in apple (Malus domestica).  Here, a comprehensive bioinformatics approach was applied to identify MdASNs in apple.  Then, plant phylogenetic tree, chromosome location, conserved protein motif, gene structure, and expression pattern of MdASNs were analyzed.  Five members were identified and distributed on 4 chromosomes with conserved GATase-7 and ASN domains.  Expression analysis indicated that all MdASNs mRNA accumulated at the highest level in reproductive organs, namely flowers or fruits, which may be associated with the redistribution of free amino acids in plant metabolic organs and reservoirs.  Additionally, most of MdASNs were dramatically up-regulated under various nitrogen supplies, especially in the aboveground part.  Taken together, MdASNs may be assigned to be responsible for the nitrogen metabolism and asparagine synthesis in apple.

Chlorophyll (Chl) biosynthesis is essential for photosynthesis and plant growth.  Glutamyl-tRNA reductase (GluTR) catalyzes glutamyl-tRNA into glutamate-1-semialdehyde (GSA) and initiates the chlorophyll biosynthesis.  Even though the main role of GluTR has been established, the effects caused by natural variations in its corresponding gene remain largely unknown.  Here, we characterized a spontaneous mutant in paddy field with Chl biosynthesis deficiency, designated as cbd1.  With intact thylakoid lamellar structure, the cbd1 plant showed light green leaves and reduced Chl and carotenoids (Cars) content significantly compared to the wild type.  By map-based gene cloning, the mutation was restricted within a 57-kb region on chromosome 10, in which an mPingA miniature inverted-repeat transposable element (MITE) inserted in the promoter region of OsHemA gene.  Both leaf color and the pigment contents in cbd1 were recovered in a complementation test, confirming OsHemA was responsible for the mutant phenotype.  OsHemA was uniquely predicted to encode GluTR and its expression level was dramatically repressed in cbd1.  Transient transformation in protoplasts demonstrated that GluTR localized in chloroplasts and a signal peptide exists in its N-terminus.  A majority of Chl biosynthesis genes, except for POR and CHLG, were down-regulated synchronously by the repression of OsHemA, suggesting that an attenuation occurred in the Chl biosynthesis pathway.  Interestingly, we found major agronomic traits involved in rice yield were statistically unaffected, except for the number of full grains per panicle was increased in cbd1.  Collectively, OsHemA plays an essential role in Chl biosynthesis in rice and its weak allele can adjust leaf color and Chls content without compromise to rice yield.