In silico characterization and comparison of the fruit ripening related beta‐ amylase (BAM) gene family in banana genome A and B

Banana is one of the most important commodities for maintaining global food security. Primary metabolic processes during the ripening of banana greatly affect post‐harvest quality, particularly in starch metabolism. The beta‐ amylase (BAM) gene family is known as a group of genes that plays an important role in starch metabolism regulation. In this study, we focused on the characterization and comparative analysis of the BAM gene family in DH Pahang and Pisang Klutuk Wulung (PKW) varieties, these being the AA and BB genomes, respectively. The sequences of BAM gene family were retrieved from the database of Musa acuminata ’DH Pahang’ and Musa balbisiana ’PKW’ genome, then structural and functional characterization was performed, followed by identification of cis‐acting elements in the BAM promoter regions. The results showed that the BAM gene family structure was relatively conserved in both genomes, and a putative BAM11 gene was found, the function of which has not been studied in other plants. Cis‐acting element analysis showed that they were distinct in the copy number and types of elements that were responsive to various phytohormones. This study suggested that the BAM genes involved in ripening are spatiotemporally regulated. However, further functional genomic analysis is required to describe the specific role and regulation of BAM genes during ripening in banana.

Association among starch storage, metabolism, related genes and growth of Moso bamboo (Phyllostachys heterocycla) shoots

Background Both underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ. However, the starch storage and utilization mechanisms during bamboo shoot growth remain unclear. This study aimed to reveal in which organs starch was stored, how carbohydrates were transformed among each organ, and how the expression of key genes was regulated during bamboo shoot growth and developmental stages which should lay a foundation for developing new theoretical techniques for bamboo cultivation. Results Based on changes of the NSC content, starch metabolism-related enzyme activity and gene expression from S0 to S3, we observed that starch grains were mainly elliptical in shape and proliferated through budding and constriction. Content of both soluble sugar and starch in bamboo shoot peaked at S0, in which the former decreased gradually, and the latter initially decreased and then increased as shoots grew. Starch synthesis-related enzymes (AGPase, GBSS and SBE) and starch hydrolase (α-amylase and β-amylase) activities exhibited the same dynamic change patterns as those of the starch content. From S0 to S3, the activity of starch synthesis-related enzyme and starch amylase in bamboo rhizome was significantly higher than that in bamboo shoot, while the NSC content in rhizomes was obviously lower than that in bamboo shoots. It was revealed by the comparative transcriptome analysis that the expression of starch synthesis-related enzyme-encoding genes were increased at S0, but reduced thereafter, with almost the same dynamic change tendency as the starch content and metabolism-related enzymes, especially during S0 and S1. It was revealed by the gene interaction analysis that AGPase and SBE were core genes for the starch and sucrose metabolism pathway. Conclusions Bamboo shoots were the main organ in which starch was stored, while bamboo rhizome should be mainly functioned as a carbohydrate transportation channel and the second carbohydrate sink. Starch metabolism-related genes were expressed at the transcriptional level during underground growth, but at the post-transcriptional level during above-ground growth. It may be possible to enhance edible bamboo shoot quality for an alternative starch source through genetic engineering.

Circadian regulation of the transcriptome in a complex polyploid crop

The circadian clock is a finely balanced time-keeping mechanism that coordinates programmes of gene expression. In polyploids, this regulation must be coordinated over multiple subgenomes. Here, we generate and analyse a high-resolution time-course dataset to investigate the circadian balance between sets of three homoeologous genes (triads) from hexaploid bread wheat. We find a large proportion of circadian triads exhibit unbalanced rhythmic expression patterns, with no specific subgenome favoured. In wheat, period lengths of rhythmic transcripts are found to be longer and have a higher level of variance than in other plant species. Biological processes under circadian control are largely conserved between wheat and Arabidopsis, however striking differences are seen in agriculturally critical processes such as starch metabolism. Together, this work highlights the ongoing selection for balance versus diversification in circadian homoeologs, and identifies clock-controlled pathways that might provide important targets for future wheat breeding.

Comparative Phosphoproteomic Analysis Reveals the Response of Starch Metabolism to High-Temperature Stress in Rice Endosperm

High-temperature stress severely affects rice grain quality. While extensive research has been conducted at the physiological, transcriptional, and protein levels, it is still unknown how protein phosphorylation regulates seed development in high-temperature environments. Here, we explore the impact of high-temperature stress on the phosphoproteome of developing grains from two indica rice varieties, 9311 and Guangluai4 (GLA4), with different starch qualities. A total of 9994 phosphosites from 3216 phosphoproteins were identified in all endosperm samples. We identified several consensus phosphorylation motifs ([sP], [LxRxxs], [Rxxs], [tP]) induced by high-temperature treatment and revealed a core set of protein kinases, splicing factors, and regulatory factors in response to high-temperature stress, especially those involved in starch metabolism. A detailed phosphorylation scenario in the regulation of starch biosynthesis (AGPase, GBSSI, SSIIa, SSIIIa, BEI, BEIIb, ISA1, PUL, PHO1, PTST) in rice endosperm was proposed. Furthermore, the dynamic changes in phosphorylated enzymes related to starch synthesis (SSIIIa-Ser94, BEI-Ser562, BEI-Ser620, BEI-Ser821, BEIIb-Ser685, BEIIb-Ser715) were confirmed by Western blot analysis, which revealed that phosphorylation might play specific roles in amylopectin biosynthesis in response to high-temperature stress. The link between phosphorylation-mediated regulation and starch metabolism will provide new insights into the mechanism underlying grain quality development in response to high-temperature stress.

Molecular Functions and Pathways of Plastidial Starch Phosphorylase (PHO1) in Starch Metabolism: Current and Future Perspectives

Starch phosphorylase is a member of the GT35-glycogen-phosphorylase superfamily. Glycogen phosphorylases have been researched in animals thoroughly when compared to plants. Genetic evidence signifies the integral role of plastidial starch phosphorylase (PHO1) in starch biosynthesis in model plants. The counterpart of PHO1 is PHO2, which specifically resides in cytosol and is reported to lack L80 peptide in the middle region of proteins as seen in animal and maltodextrin forms of phosphorylases. The function of this extra peptide varies among species and ranges from the substrate of proteasomes to modulate the degradation of PHO1 in Solanum tuberosum to a non-significant effect on biochemical activity in Oryza sativa and Hordeum vulgare. Various regulatory functions, e.g., phosphorylation, protein–protein interactions, and redox modulation, have been reported to affect the starch phosphorylase functions in higher plants. This review outlines the current findings on the regulation of starch phosphorylase genes and proteins with their possible role in the starch biosynthesis pathway. We highlight the gaps in present studies and elaborate on the molecular mechanisms of phosphorylase in starch metabolism. Moreover, we explore the possible role of PHO1 in crop improvement.