Identification of the arl1 locus controlling leaf rolling and its application in maize breeding.

Increasing planting density is one of the most important strategies for generating higher maize yields. Moderate leaf rolling decreases mutual shading of leaves and increases the photosynthesis of the population and hence increases the tolerance for high-density planting. Few genes that control leaf rolling in maize have been identified, however, and their applicability for breeding programs remains unclear. Here we identified a maize abaxially rolled leaf1 (arl1) mutant with extreme abaxially rolled leaves and found that the size of the bulliform cells within the adaxial leaf blade surface increased in the arl1 mutant. Bulk segregation analysis mapping in an F₂ population derived from a single cross between arl1 and inbred line Gui18421 with normal leaves identified the arl1 locus on chromosome 2. Sequential fine-mapping delimited the arl1 locus to a 233.56-kb genomic interval containing three candidate genes. Sequence alignment between arl1 and Gui18421 identified an 8-bp insertion in the coding region of Zm00001eb082500, which led to a frame shift causing premature transcription termination in arl1 mutant. Meanwhile, both deep sequencing and Sanger sequencing showed that Zm00001eb082520 was present in Gui18421 but was absent in arl1. A pair of near isogenic lines (NILs) carrying the Gui18421 allele (NIL^Gui18421) and the arl1 allele (NIL ^arl1 ) were developed, and the leaves of NIL ^arl1 plants had greater light transmission and photosynthetic rate in the middle and lower canopy than did those of NIL^Gui18421 plants under high-density planting. Furthermore, NIL ^arl1 had a higher seed setting rate, more kernels per ear, and an increased kernel weight per ear than NIL^Gui18421, and the grain yield of NIL ^arl1 was not affected as the planting density increased, suggesting that the arl1 locus can be used for genetic improvement of high-density planting tolerance. Taken together, the identification of arl1 and evaluation of yield-related traits for NIL^Gui18421 and NIL ^arl1 provide an excellent target for future maize improvement.

Supplementary information: The online version contains supplementary material available at 10.1007/s11032-024-01534-0.