pGVG: a new Gateway-compatible vector for transformation of sugarcane and other monocot crops

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.

Silencing ScGUX2 reduces xylan glucuronidation and improves biomass saccharification in sugarcane

There is an increasing need for renewable energy sources to replace part of our fossil fuel-based economy and reduce greenhouse gas emission. Sugarcane bagasse is a prominent feedstock to produce cellulosic bioethanol, but strategies are still needed to improve the cost-effective exploitation of this potential energy source. In model plants, it has been shown that GUX genes are involved in cell wall hemicellulose decoration, adding glucuronic acid substitutions on the xylan backbone. Mutation of GUX genes increases enzyme access to cell wall polysaccharides, reducing biomass recalcitrance in Arabidopsis thaliana. Here, we characterized the sugarcane GUX genes and silenced GUX2 in commercial hybrid sugarcane. The transgenic lines had no penalty in development under greenhouse conditions. The sugarcane GUX1 and GUX2 enzymes generated different patterns of xylan glucuronidation, suggesting they may differently influence the molecular interaction of xylan with cellulose and lignin. Studies using biomass without chemical or steam pretreatment showed that the cell wall polysaccharides, particularly xylan, were less recalcitrant in sugarcane with GUX2 silenced than in WT plants. Our findings suggest that manipulation of GUX in sugarcane can reduce the costs of second-generation ethanol production and enhance the contribution of biofuels to lowering the emission of greenhouse gases.

CRISPR technology towards genome editing of the perennial and semi-perennial crops citrus, coffee and sugarcane

Gene editing technologies have opened up the possibility of manipulating the genome of any organism in a predicted way. CRISPR technology is the most used genome editing tool and, in agriculture, it has allowed the expansion of possibilities in plant biotechnology, such as gene knockout or knock-in, transcriptional regulation, epigenetic modification, base editing, RNA editing, prime editing, and nucleic acid probing or detection. This technology mostly depends on in vitro tissue culture and genetic transformation/transfection protocols, which sometimes become the major challenges for its application in different crops. Agrobacterium-mediated transformation, biolistics, plasmid or RNP (ribonucleoprotein) transfection of protoplasts are some of the commonly used CRISPR delivery methods, but they depend on the genotype and target gene for efficient editing. The choice of the CRISPR system (Cas9, Cas12), CRISPR mechanism (plasmid or RNP) and transfection technique (Agrobacterium spp., PEG solution, lipofection) directly impacts the transformation efficiency and/or editing rate. Besides, CRISPR/Cas technology has made countries rethink regulatory frameworks concerning genetically modified organisms and flexibilize regulatory obstacles for edited plants. Here we present an overview of the state-of-the-art of CRISPR technology applied to three important crops worldwide (citrus, coffee and sugarcane), considering the biological, methodological, and regulatory aspects of its application. In addition, we provide perspectives on recently developed CRISPR tools and promising applications for each of these crops, thus highlighting the usefulness of gene editing to develop novel cultivars.

Reduction of ethylene biosynthesis in sugarcane induces growth and investment in the non-enzymatic antioxidant apparatus

Lower ethylene production in sugarcane results in plants with higher stature, expression of growth-promoting genes, higher photosynthetic rate, and increased antioxidant compounds. The hormone ethylene is involved in critical processes in sugarcane, such as the growth and accumulation of sucrose. The lack of mutants for ethylene biosynthesis or signaling genes makes it difficult to understand the role of this phytohormone throughout sugarcane development. This study aimed to evaluate the physiology and development of sugarcane plants with low ethylene production. To achieve this goal, we used RNA interference to silence three genes, ScACS1, ScACS2, and ScACS3, encoding 1-aminocyclopropane-1-carboxylic acid synthases (ACS), responsible for a limiting step of the ethylene biosynthesis pathway. Sugarcane plants with reduced ethylene levels presented increased growth, faster germination of lateral gems, and activation of non-enzymatic antioxidant mechanisms. We observed an augmentation in the expression of ScACO5, which encodes the final enzyme regulating ethylene biosynthesis, and ScERF1, encoding a transcription factor, linked to the ethylene response. The increase in plant height was correlated with higher expression of ScPIF3, ScPIF4, and ScPIF5, which encode for transcription factors related to growth induction. Interestingly, there was also an increase in the expression of the ScGAI gene, which encodes a DELLA protein, a growth repressor. The final content of sucrose in the stems was not affected by the low levels of ethylene, although the rate of CO₂ assimilation was reduced. This study reports for the first time the impacts of low endogenous production of ethylene in sugarcane and provides helpful insights on the molecular mechanisms behind ethylene responses.

Visualization of Suberization and Lignification in Sugarcane

Cell wall biopolymers are major factors responsible for the high recalcitrance of sugarcane biomass. The study of suberization and lignification mechanisms in sugarcane and of the networks that control biosynthesis of these polymers will contribute to the biotechnological improvement of this crop. Here, we describe experiments that allow the visualization of the suberization and lignification mechanism in response to mechanical injury in sugarcane.