A Wild Allele of Pyrroline-5-Carboxylate Synthase1 Leads to Proline Accumulation in Spikes and Leaves of Barley Contributing to Improved Performance Under Reduced Water Availability

Abstract

Water stress (WS) during spike development strongly affects final grain yield and grain quality in cereals. Proline, an osmoprotectant amino-acid, may contribute to alleviating the effects of cell and tissue dehydration. We studied five spring barley genotypes contrasting in their drought response, including two introgression lines, S42IL-143 and S42IL-141, harboring a Pyrroline-5-carboxylate synthase1- P5cs1 allele originating from the wild barley accession ISR42-8. We tested the hypothesis that barley genotypes harboring a wild allele at P5cs1 locus are comparatively more drought-tolerant at the reproductive stage by inducing proline accumulation in their immature spikes. At the booting stage, we subjected plants to well-watered and WS treatments until physiological maturity. Several morpho-physiological traits had significant genotype by treatment interaction and reduction under WS. Varying levels of genotypic proline accumulation and differences in WS tolerance were observed. Spike proline accumulation was higher than leaf proline accumulation for all genotypes under WS. Also, introgression lines carrying a wild allele at P5cs1 locus had a markedly higher spike and leaf proline content compared with the other genotypes. These introgression lines showed milder drought symptoms compared with elite genotypes, remained photosynthetically active under WS, and maintained their intrinsic water use efficiency. These combined responses contributed to the achievement of higher final seed productivity. Magnetic resonance imaging (MRI) of whole spikes at the soft dough stage showed an increase in seed abortion among the elite genotypes compared with the introgression lines 15 days after WS treatment. Our results suggest that proline accumulation at the reproductive stage contributes to the maintenance of grain formation under water shortage.

Detection and Verification of QTL for Salinity Tolerance at Germination and Seedling Stages Using Wild Barley Introgression Lines

“…This IL seems to be a promising genomic region carrying a valuable novel allele for salinity tolerance. Also, the ILs S42 IL-141 and S42 IL-143 on 1H showed favorable line main effect of RSR, these two lines harboring a Pyrroline-5-carboxylate synthase1-P5cs1 allele derived from the wild barley accession ISR42-8 which showed high proline accumulation [50], and displayed less severe wilting under drought stress [25].…”

“…In this way, by using genetic approaches, new genes and/or new alleles associated with enhanced salinity tolerance at known loci present in wild genotypes could be mapped and targeted for introgression. In the past decade, a number of studies have investigated the S42ILs library under different environmental conditions including drought, phosphorus and nitrogen deficiency [21][22][23][24][25][26]. These experiments identified beneficial exotic QTL alleles, which were contributed significantly to the enhancement of agronomic, biotic, and abiotic stress tolerance-related traits.…”

Proline-Mediated Drought Tolerance in the Barley (Hordeum vulgare L.) Isogenic Line Is Associated with Lateral Root Growth at the Early Seedling Stage

“…An increase in proline causes changes in the osmotic potential and cell turgor pressure, promoting the accumulation of potassium and other solutes in the larger cell vacuole [ 56 ]. Several other studies indicate that higher leaf and root proline concentrations are associated with greener leaves, cell turgor, cell membrane stability, and improved whole-plant performance in many crop species, including barley [ 57 , 58 , 59 , 60 ].…”

“…A more than 5-fold increase in spike and leaf proline accumulation occurred in barley introgressions bearing the wild allele of pyrroline-5-carboxylate synthase1 , which contributed to improved seed yield and whole-plant performance under reduced water availability [ 60 ]. In the current study, water stress caused more than a 2-fold increase in the leaf and root proline concentration in NIL 143 compared with Barke and Scarlett ( Table 1 and Figure 1 ).…”

“…The stored leaf, stem, and root tissue samples were manually crushed into a fine powder using a ceramic mortar and pestle in liquid nitrogen. The extraction of proline from each tissue was performed by adopting the colorimetric proline determination method described by Bates and Waldren (1973) [ 74 ] and Frimpong et al (2021) [ 60 ] with slight modifications. Acid-ninhydrin was first prepared by warming 2.5 g of ninhydrin in 60 mL of glacial acetic acid and 40 mL of 6 M phosphoric acid, with vigorous agitation using a magnetic stirrer until completely dissolved.…”