Rice Biofortification With Zinc and Selenium: A Transcriptomic Approach to Understand Mineral Accumulation in Flag Leaves

Abstract

Human malnutrition due to micronutrient deficiencies, particularly with regards to Zinc (Zn) and Selenium (Se), affects millions of people around the world, and the enrichment of staple foods through biofortification has been successfully used to fight hidden hunger. Rice (Oryza sativa L.) is one of the staple foods most consumed in countries with high levels of malnutrition. However, it is poor in micronutrients, which are often removed during grain processing. In this study, we have analyzed the transcriptome of rice flag leaves biofortified with Zn (900 g ha −1), Se (500 g ha −1), and Zn-Se. Flag leaves play an important role in plant photosynthesis and provide sources of metal remobilization for developing grains. A total of 3170 differentially expressed genes (DEGs) were identified. The expression patterns and gene ontology of DEGs varied among the three sets of biofortified plants and were limited to specific metabolic pathways related to micronutrient mobilization and to the specific functions of Zn (i.e., its enzymatic co-factor/coenzyme function in the biosynthesis of nitrogenous compounds, carboxylic acids, organic acids, and amino acids) and Se (vitamin biosynthesis and ion homeostasis). The success of this approach should be followed in future studies to understand how landraces and other cultivars respond to biofortification.

Post-transcriptional regulation of 2-acetyl-1-pyrroline (2-AP) biosynthesis pathway, silicon, and heavy metal transporters in response to Zn in fragrant rice

“…Zn is important for the physiological and biochemical functions of plants. Therefore, previous research in plants was focused on transcriptional changes in response to Zn to identify the molecular pathways and the transcription factors that control these pathways ( Schvartzman et al, 2018 ; Roda et al, 2020 ; Bao et al, 2021 ). However, post-transcriptional regulation of gene expression in response to Zn is largely ignored.…”

Transcriptomics View over the Germination Landscape in Biofortified Rice

“…The few studies where seed germination was evaluated in biofortified rice lines indicate that most traits (e.g., LPA, high-ascorbate, high-tryptophan) have negative effects on the germination behavior [ 31 , 45 , 46 , 69 ], while agronomic approaches with micronutrient supplementation (e.g., Zn, Se) can also have beneficial effects depending on dosage and type of treatment [ 34 , 35 ]. When these positive outcomes on germination were reported, transcriptomics studies evidenced also the upregulation of genes with specific roles in this process, such as QLTG3-1, reported to improve germination under low temperatures [ 58 ], part of a QTL with specific functions in weakening seed tissues during germination [ 84 , 123 ]. On the other hand, enhanced tryptophan production in rice seeds led to germination penalties, due to interferences between the IAA and auxin pathways [ 69 ].…”

“…These studies are important because before selecting suitable genes for the biofortification program, an in-depth functional characterization of expression patterns during micronutrient uptake, transport, and storage is required. Given this, a recent study investigated the transcriptional changes in rice flag leaves following agronomic biofortification with Zn and Se delivered through foliar spraying [ 58 ]. Flag leaves play important roles in grain filling, especially in the biosynthesis and translocation of minerals to the seeds [ 59 ].…”

“…The study evidenced a relatively low number of differentially expressed genes (DEGs) with significant fold changes in response to the imposed treatments. The reasoning behind this appears to be associated with a limited impact on specific pathways (e.g., mineral absorption, translocation) or post-transcriptional regulation [ 58 ]. A relevant upregulated (3.2-fold) DEG ( Os03g0103300 ) associated with seed germination encodes a QLTG-3-1 protein targeted for low-temperature germinability.…”

Improving nutrition through biofortification–A systematic review

“…Hence, genomics (omics technology of genes) is important since it presents the opportunity to study these specific genes and design suitable ways of improving and inducing them into crops (138,150). Transcriptomics (omics technology of transcripts) aids in conducting fullspectrum analysis to identify a specific expressed gene (20,151,152). Proteomics (omics technology of proteins) helps to understand the role of proteins in nutrient synthesis, uptake and transport pathways (21,22).…”