Allantoin improves salinity tolerance in Arabidopsis and rice through synergid activation of abscisic acid and brassinosteroid biosynthesis

Soil salinity stress is one of the major bottlenecks for crop production. Although, allantoin is known to be involved in nitrogen metabolism in plants, yet several reports in recent time indicate its involvement in various abiotic stress responses including salinity stress. However, the detail mechanism of allantoin involvement in salinity stress tolerance in plants is not studied well. Moreover, we demonstrated the role of exogenous application of allantoin as well as increased concentration of endogenous allantoin in rendering salinity tolerance in rice and Arabidopsis respectively, via., induction of abscisic acid (ABA) and brassinosteroid (BR) biosynthesis pathways. Exogenous application of allantoin (10 mu M) provides salt-tolerance to salt-sensitive rice genotype (IR-29). Transcriptomic data after exogenous supplementation of allantoin under salinity stress showed induction of ABA (OsNCED1) and BR (Oscytochrome P450) biosynthesis genes in IR-29. Further, the key gene of allantoin biosynthesis pathway i.e., urate oxidase of the halophytic species Oryza coarctata was also found to induce ABA and BR biosynthesis genes when over-expressed in transgenic Arabidopsis. Thus, indicating that ABA and BR biosynthesis pathways were involved in allantoin mediated salinity tolerance in both rice and Arabidopsis. Additionally, it has been found that several physio-chemical parameters such as biomass, Na+/K+ ratio, MDA, soluble sugar, proline, allantoin and chlorophyll contents were also associated with the allantoin-mediated salinity tolerance in urate oxidase overexpressed lines of Arabidopsis. These findings depicted the functional conservation of allantoin for salinity tolerance in both plant clades. Key messagePhytohormonal pathways (abscisic acid and brassinosteroid) are involved in allantoin mediated salinity stress tolerance response in both monocot and dicot.

Automated summary

Soil salinity stress is a major obstacle for crop production. Recent reports indicate that allantoin is involved in various abiotic stress responses, including salinity stress. However, the detailed mechanism of allantoin's involvement in salinity stress tolerance in plants is not well studied. This study demonstrates the role of exogenous application of allantoin and increased endogenous allantoin concentration in enhancing salinity tolerance in rice and Arabidopsis, through the induction of ABA and BR biosynthesis pathways.