Abstract
Brachiaria (Trin.) Griseb. (syn. Urochloa P. Beauv.) is a C4 grass genus belonging to the Panicoideae. Native to Africa, these grasses are now widely grown as forages in tropical areas worldwide and are the subject of intensive breeding, particularly in South America. Tolerance to abiotic stresses such as aluminum and drought are major breeding objectives. In this study, we present the transcriptomic profiling of leaves and roots of three Brachiaria interspecific hybrid genotypes with the onset of water stress, Br12/3659-17 (gt-17), Br12/2360-9 (gt-9), and Br12/3868-18 (gt-18), previously characterized as having good, intermediate and poor tolerance to drought, respectively, in germplasm evaluation programs. RNA was extracted from leaf and root tissue of plants at estimated growing medium water contents (EWC) of 35, 15, and 5%. Differentially expressed genes (DEGs) were compared between different EWCs, 35/15, 15/5, and 35/5 using DESeq2. Overall, the proportions of DEGs enriched in all three genotypes varied in a genotype-dependent manner in relation to EWC comparison, with intermediate and sensitive gt-9 and gt-18 being more similar to each other than to drought tolerant gt-17. More specifically, GO terms relating to carbohydrate and cell wall metabolism in the leaves were enriched by up-regulated DEGs in gt-9 and gt-18, but by down-regulated DEGs in gt-17. Across all genotypes, analysis of DEG enzyme activities indicated an excess of down-regulated putative apoplastic peroxidases in the roots as water stress increased. This suggests that changes in root cell-wall architecture may be an important component of the response to water stress in Brachiaria.
Highlights
For healthy development, growth and reproduction plants need sufficient water
Identified differences between tissues and genotypes do not necessarily indicate overall presences or absences of particular kinds of biological responses, just their detections at defined assay points. The outcomes of these studies can be valuable for indicating variability between genotypes and so point to areas which may be fruitful for further research focus in the contexts of both plant biology and, in the context of this study, the exploitation of Brachiaria genetic variability for forage grass improvement
We have undertaken a study comparing differential geneexpression, in relation to the onset of water stress, across three Brachiaria hybrid genotypes with contrasting physiological responses to water deficit and identified a range of Gene Ontology (GO) terms linked to biological responses in leaves and roots
Summary
Growth and reproduction plants need sufficient water Due to their sessile nature, plants often encounter unfavorable environmental conditions during their life cycles and water stress is a major environmental factor that limits crop growth and yield. Urochloa P.Beauv.) is a C4 grass genus belonging to the Panicoideae (Renvoize et al, 1996) This genus includes several species which are important as agricultural grasses, notably B. decumbens Stapf., B. brizantha These grasses, native to Africa, are widely grown in the form of individual species and hybrids, as forage grasses in tropical areas worldwide (KellerGrein et al, 1996). Particular aims of breeding for these grasses have been to maintain and improve forage quality while increasing tolerances to abiotic stresses such as aluminum (acid soils) and drought, in addition to disease and pest resistance
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