Periodic Reporting for period 1 - LGSMAIZE (Engineering of low germination stimulant production to control witchweed infection in maize in Sub-Saharan Africa)
Periodo di rendicontazione: 2023-09-01 al 2025-02-28
The parasitic witchweeds, such as Striga hermonthica and Striga asiatica, pose an enormous threat for production of cereal crops, such as sorghum, millet and maize, in the African continent, threatening the livelihood of millions of people, especially in sub-Saharan Africa. Striga seeds lay dormant in the soil until their germination is triggered by strigolactones (SLs), signaling compounds exuded by roots of plants, including maize. Maize exudes at least six different SLs from its roots into the rhizosphere, two of which were earlier identified as zealactone and zeapyranolactone.
In ERC Advanced project CHEMCOMRHIZO we elucidated the identity of the other maize strigolactones and demonstrated that there is natural variation in the germination stimulant composition in the root exudate of maize varieties and that this can result in full Striga resistance. We also elucidated the entire biosynthetic pathway of all maize strigolactones. In LGSMAIZE, we create knock-out lines in these strigolactone biosynthetic genes in an elite African maize variety in collaboration with the CGIAR institute CIMMYT, to deliver the proof-of-concept that Striga resistance can be introduced into maize. In parallel, we analyse existing maize varieties with different blends of strigolactones for their microbiome recruitment.
In ERC Advanced project CHEMCOMRHIZO we elucidated the identity of the other maize strigolactones and demonstrated that there is natural variation in the germination stimulant composition in the root exudate of maize varieties and that this can result in full Striga resistance. We also elucidated the entire biosynthetic pathway of all maize strigolactones. In LGSMAIZE, we create knock-out lines in these strigolactone biosynthetic genes in an elite African maize variety in collaboration with the CGIAR institute CIMMYT, to deliver the proof-of-concept that Striga resistance can be introduced into maize. In parallel, we analyse existing maize varieties with different blends of strigolactones for their microbiome recruitment.
The genes to be edited were selected in consultation with CIMMYT. We decided to edit CCD7, CCD8, MAX1, CYP706, MET, and 2 strigolactone ABC transporter gene candidates. We decided to do this both in minimaize and CML536, an elite African maize variety. The process of gene editing proved to be challenging also because contractual issues had to be solved with Corteva on the fly. A first batch of seeds of gene edited lines is anticipated to be sent to us in August 2025. The rest of the lines is anticipated by the beginning of 2026.
In parallel, we have carried out experiments with a number of maize genotypes differing in strigolactone profile. These genotypes were grown in a natural soil substrate and rhizosphere soil was collected, DNA extracted and 16S, ITS and AM fungi metabarcoding carried out. We are currently analysing these data, and preparing a publication about the effect of differences in the maize strigolactone blend on microbiome recruitment.
A new grant was obtained by the PI as collaborator in a Swiss National Science Foundation grant, coordinated by the group of Marcel van der Heijden of Zurich University. In this grant we will further characterize the gene edited lines for AM fungi recruitment in greenhouse and field experiments. This will result in a number of additional publications.
In parallel, we have carried out experiments with a number of maize genotypes differing in strigolactone profile. These genotypes were grown in a natural soil substrate and rhizosphere soil was collected, DNA extracted and 16S, ITS and AM fungi metabarcoding carried out. We are currently analysing these data, and preparing a publication about the effect of differences in the maize strigolactone blend on microbiome recruitment.
A new grant was obtained by the PI as collaborator in a Swiss National Science Foundation grant, coordinated by the group of Marcel van der Heijden of Zurich University. In this grant we will further characterize the gene edited lines for AM fungi recruitment in greenhouse and field experiments. This will result in a number of additional publications.
Our study is the first in which strigolactone biosynthesis in any plant species is systematically being altered through gene editing, and the consequences of altered strigolactone profiles being analysed for both Striga infection and microbiome recruitment. If the gene editing results in Striga resistance in the African maize variety that we used, this could potentially result in a game changer in the fight against the Striga scorge in maize, as well as pave the way for similar approaches in other crops suffering from parasitic weeds. The possible effects on microbiome recruitment will further unravel the importance of host signalling in microbiome recruitment and may pave the way to crop breeding for optimized use of thye microbiome in agriculture.