The Genetics and Genome-Wide Screening of Regrowth Loci, a Key Component of Perennialism in Zea diploperennis

Abstract

Perennialism is common among the higher plants, yet little is known about its inheritance. Previous genetic studies of the perennialism in Zea have yielded contradictory results. In this study, we take a reductionist approach by specifically focusing on one trait: regrowth (the plant’s ability to restart a new life cycle after senescence on the same body). To address this, six hybrids were made by reciprocally crossing perennial Zea diploperennis Iltis, Doebley & R. Guzman with inbred lines B73 and Mo17 and Rhee Flint, a heirloom variety, of Z . mays L. ssp. mays . All the F 1 plants demonstrated several cycles of growth, flowering, senescence and regrowth into normal flowering plants, indicating a dominant effect of the Z. diploperennis alleles. The regrowability ( i.e. , the plants’ ability to regrow after senescence) was stably transmitted to progeny of the hybrids. Segregation ratios of regrowth in the F 2 generations are consistent with the trait controlled by two dominant, complementary loci, but do not exclude the influence of other modifiers or environment. Genome-wide screening with genotyping-by-sequencing technology indicated two major regrowth loci, regrowth 1 ( reg1 ) and regrowth 2 ( reg2 ), were on chromosomes 2 and 7, respectively. These findings lay the foundation for further exploration of the molecular mechanism of regrowth in Z. diploperennis . Importantly, our data indicate that there is no major barrier to transferring this trait into maize or other grass crops for perennial crop development with proper technology, which enhances sustainability of grain crop production in an environmentally friendly way.

QTL Map of Early- and Late-Stage Perennial Regrowth in Zea diploperennis

“…The second is located on the long arm of chromosome 8 near position 150 Mb on the P39 physical map, and will be referred to as regrowth3 ( reg3 ). The regrowth2 locus on the short arm of chromosome 7 ( Ma et al, 2019 ) did not show significant differences in SNP-index between the two sequenced bulks.…”

“…Two loci displayed higher SNP-indices in the RG compared to the NRG bulk ( Figure 2 ). The first is on the short arm of chromosome 2, and corresponds to the dominant QTL previously identified as regrowth1 ( reg1 ) ( Ma et al, 2019 ). The second is located on the long arm of chromosome 8 near position 150 Mb on the P39 physical map, and will be referred to as regrowth3 ( reg3 ).…”

“…The first two perennial regrowth QTL in Z. diploperennis were named regrowth1 and regrowth2 and lie near 33.0 Mb on chromosome 2 and 4.2 Mb on chromosome 7 using B73v4 coordinates ( Ma et al, 2019 ). They were described as dominant, fully penetrant, and complementary to one another.…”

“…We found two genomic regions associated with regrowth using a modified bulk segregant analysis approach called QTL-seq ( Michelmore et al, 1991 ; Takagi et al, 2013 ) in combination with targeted PCR-based genotyping. One QTL maps to the same location as reg1 ( Ma et al, 2019 ), while a second, previously unreported QTL maps to chromosome 8 and shows a strong effect in the later stages of regrowth.…”

“…These are important first steps but it remains unclear whether lines bred for rhizome formation will demonstrate perennial regrowth. A recent study took a different approach of mapping genes that promote regrowth itself by crossing domesticated maize to its close perennial ancestor of maize ( Zea mays L.) called Zea diploperennis ( Iltis et al, 1979 ; Ma et al, 2019 ). Regrowth is generally scored as the presence of new branches at the base of the plant after the plant has flowered and senesced.…”