Genetic modification of PIN genes induces causal mechanisms of stay-green drought adaptation phenotype

Abstract

The stay-green trait is recognised as a key drought adaptation mechanism in cereals worldwide. Stay-green sorghum plants exhibit delayed senescence of leaves and stems, leading to prolonged growth, a reduced risk of lodging and higher grain yield under end-of-season drought stress. More than 45 quantitative trait loci (QTL) associated with stay-green have been identified, including two major QTL (Stg1 and Stg2). However, none of the contributing genes that regulate functional stay-green are known. Here we show that the PIN FORMED family of auxin efflux carriers induce some of the causal mechanisms driving the stay-green phenotype in sorghum, with SbPIN4 and SbPIN2 located in Stg1 and Stg2, respectively. We found that 9 of 11 sorghum PIN genes aligned with known stay-green QTL. In transgenic studies, we demonstrated that PIN genes located within the Stg1 (SbPIN4), Stg2 (SbPIN2) and Stg3b (SbPIN1) QTL regions acted pleiotropically to modulate canopy development, root architecture and panicle growth in sorghum, with SbPIN1, SbPIN2 and SbPIN4 differentially expressed in various organs relative to the non stay-green control. The emergent consequence of such modifications in canopy and root architecture is a stay-green phenotype. Crop simulation modelling shows that the SbPIN2 phenotype can increase grain yield under drought.

Unveiling shared genetic regulators for plant architectural and biomass yield traits in sorghum

“…Four major QTLs, namely Stg1-4 derived from BTx642, have been identified. Detailed analysis revealed the presence of multiple PIN FORMED family of auxin efflux carrier genes within these QTLs, such as the Stg1 ( SbPIN4 ), Stg2 ( SbPIN2 ), and Stg3b ( SbPIN1 ) (Borrell et al ., 2022). Similarly, cytokinin biosynthetic genes delay senescence in Arabidopsis and sorghum, probably due to increased activity of cell wall invertase ( CWINV ), a gene that affects the leaf source/sink balance (Markovich et al ., 2017).…”

“…Recent studies have demonstrated the significant role of both cytokinin and auxin in stay-green phenotypes in sorghum (Markovich et al ., 2017; Borrell et al ., 2022). Stay-green traits enable plants to retain green leaves and stems, thus maintaining longer growth during the end of the drought season (Borrell et al ., 2000).…”

Seminal root angle is associated with root system architecture in durum wheat

“…Similarly, previous studies in sorghum have also reported co‒ locations of genetic loci for stay‒green traits and root angle (Mace et al, 2012; Borrell et al, 2014). Since one of the important mechanisms underlying stay‒green is associated with increased post‒flowering water uptake in terminal drought environments, a root system with a steep angle should result in a deep rooting system that enhances access to deep soil water (Manschadi, Christopher, Devoil, & Hammer, 2006; Singh, van Oosterom, Jordan, & Hammer, 2012; Borrell et al, 2014; Borrell et al, 2022). Therefore, SRA may be a major determinant of the mature RSA, making it a promising candidate for selection that can be conducted in the early growth stages to accelerate the breeding process.…”

ThePIN2ortholog in barley modifies root gravitropism and architecture without impacting the shoot

“…Indirect effects can be seen in the dynamic balance of allometry where growth of one organ influences another. For example, the canopy has an allometric relationship with the root system, where increases in the canopy biomass correlates with increased root biomass (Borrell et al 2022). As PIN2 expression is almost exclusively within the roots, the possibility of root specific architectural changes, independent of above- and below-ground allometry, provides an interesting subject for investigation (Müller et al 1998).…”