The BAM7 gene in Zea mays encodes a protein with similar structural and catalytic properties to Arabidopsis BAM2

Transcription factor MdGTL1a accelerates starch degradation by promoting the MdBam8 expression in postharvest apple fruit

Starch degradation plays a central role in fruit ripening. The β-amylase (Bam) catalysts starch degradation of apple fruit. However, the molecular mechanism regulating Bam gene expression in apples remains unclear. Using yeast one-hybrid library screening, we identified a transcription factor MdGTL1a that directly binds to the MdBam8 promoter. This bind was verified by using an electrophoretic mobility shift assay and confirmed to enhance the promotor activity of MdBam8 by promoter-β-glucuronidase transactivation assay. Transient over-expression of MdGTL1a activated MdBam8 expression and further enhanced starch degradation in apple flesh. Subcellular localization analyses in tobacco protoplasts demonstrated that the nucleus was the exclusive location of the MdGTL1a-GFP fusion protein. Exogenous salicylic acid treatment decreased MdGTL1a expression and resulted in higher starch content in apples, which was consistent with the fruit ripening. It is concluded that salicylic acid treatment could enhance apple storage quality by inhibiting starch degradation through a crucial transcription factor, MdGTL1a.

Leaf starch degradation by β-amylase ZmBAM8 influences drought tolerance in maize

As a typical C4 plant and important crop worldwide, maize is susceptible to drought. In maize, transitory starch (TS) turnover occurs in the vascular bundle sheath of leaves, differing from that in Arabidopsis (a C3 plant). This process, particularly its role in drought tolerance and the key starch-hydrolyzing enzymes involved, is not fully understood. We discovered that the expression of the β-amylase (BAM) gene ZmBAM8 is highly upregulated in the drought-tolerant inbred line Chang7-2t. Inspired by this finding, we systematically investigated TS degradation in maize lines, including Chang7-2t, Chang7-2, B104, and ZmBAM8 overexpression (OE) and knockout (KO) lines. We found that ZmBAM8 was significantly induced in the vascular bundle sheath by drought, osmotic stress, and abscisic acid. The stress-induced gene expression and chloroplast localization of ZmBAM8 align with the tissue and subcellular sites where TS turnover occurs. The recombinant ZmBAM8 was capable of effectively hydrolyzing leaf starch. Under drought conditions, the leaf starch in ZmBAM8-OE plants substantially decreased under light, while that in ZmBAM8-KO plants did not decrease. Compared with ZmBAM8-KO plants, ZmBAM8-OE plants exhibited increased drought tolerance. Our study provides insights into the significance of leaf starch degradation in C4 crops and contributes to the development of drought-resistant maize.

Maize β-amylase7 encodes two proteins using alternative transcriptional start sites: nuclear BAM7 and plastidic BAM2

An unusual β-amylase7 (BAM7) gene in some angiosperms, including grasses such as maize (Zea mays), appears to encode two functionally distinct proteins; a nuclear-localized transcription factor (BAM7) and a plastid-localized starch hydrolase (BAM2). In Arabidopsis (Arabidopsis thaliana), these two proteins are encoded by separate genes on different chromosomes but their physiological functions are not well established. Using the maize BAM7 gene as a model, we detected two populations of transcripts by 5'-RACE that encode the predicted proteins. The two transcripts are apparently synthesized independently using separate core promoters about 1 kb apart, the second of which is located in the first intron of the full-length gene. The N-terminus of the shorter protein, ZmBAM7-S, begins near the 3' end of the first intron of ZmBAM7-L and starts with a predicted chloroplast transit peptide. We previously showed that ZmBAM7-S is catalytically active with properties like those of AtBAM2. Here, we report that ZmBAM7-S targets green fluorescent protein to plastids. The transcript encoding the longer protein, ZmBAM7-L, encodes an additional DNA-binding domain containing a functional nuclear localization signal. This putative dual-function gene originated at least 400 Mya, prior to the emergence of ferns, and has persisted in some angiosperms that lack a separate BAM2 gene. It appears to have been duplicated and subfunctionalized in at least four lineages of land plants, resulting in two genes resembling Arabidopsis BAM2 and BAM7. Targeting of two products from a single gene to different subcellular locations is not uncommon in plants, but it is unusual when they are predicted to serve completely different functions in the two locations.

α-SAS: an integrative approach for structural modeling of biological macromolecules in solution

Modern small-angle scattering (SAS) experiments with neutrons (SANS) or X-rays (SAXS) combined with contrast variation provide comprehensive information about the structure of large multicomponent macromolecules in solution and allow the size, shape and relative arrangement of each component to be mapped out. To obtain such information, it is essential to perform well designed experiments, in which all necessary steps, from assessing sample suitability to structure modeling, are properly executed. This paper describes α-SAS, an integrative approach that is useful for effectively planning a biological contrast-variation SAS experiment. The accurate generation of expected experimental intensities using α-SAS allows the substantial acceleratation of research into the structure and function of biomacromolecules by minimizing the time and costs associated with performing a SAS experiment. The method is validated using a few basic structures with known analytical expressions for scattering intensity and using experimental SAXS data from Arabidopsis β-amylase 1 protein and SANS data from the histidine kinase–Sda complex and from human dystrophin without and with a membrane-mimicking nanodisk. Simulation of a SANS contrast-variation experiment is performed for synthetic nanobodies that effectively neutralize SARS-CoV-2.