ZmCCT9 enhances maize adaptation to higher latitudes

Area of Science:

• Genetics
• Plant Biology
• Evolutionary Biology

Background:

• Maize (Zea mays) originated in Mexico and spread widely across the Americas, a feat unusual for crops due to latitudinal adaptation challenges.
• The genetic mechanisms enabling maize's extensive latitudinal adaptation remain largely uncharacterized.

Purpose of the Study:

• To investigate the genetic basis of maize's widespread latitudinal adaptation.
• To identify the genes and regulatory elements controlling flowering time in maize for adaptation to different latitudes.

Main Methods:

• Positional cloning and association mapping to identify quantitative trait loci.
• CRISPR/Cas9 gene editing to study gene function.
• Population genetics analyses to understand evolutionary history.
• Analysis of transposable element activity and its role in gene regulation.

Main Results:

• A Harbinger-like transposable element 57 kb upstream of ZmCCT9 was identified as a flowering-time quantitative trait locus.
• This element represses ZmCCT9 expression, promoting flowering under long days; its knockout causes early flowering.
• ZmCCT9 regulates the florigen ZCN8, influencing flowering time under long days.
• Sequential insertions of Harbinger-like and CACTA-like transposons at ZmCCT9 and ZmCCT10, respectively, were targeted by selection for higher latitude adaptation.

Conclusions:

• Transposable element activity and selection played a crucial role in maize's adaptation to diverse latitudes.
• The dynamic maize genome facilitated adaptation over a 90° latitudinal range during the pre-Columbian era.
• Understanding these genetic mechanisms provides insights into crop evolution and adaptation strategies.