Positional cloning and characterization reveal the role of a miRNA precursor gene ZmLRT in the regulation of lateral root number and drought tolerance in maize

Lateral roots play essential roles in drought tolerance in maize(Zea mays L.). However, the genetic basis for the variation in the number of lateral roots in maize remains elusive. Here, we identified a major quantitative trait locus(QTL),q LRT5-1, controlling lateral root number using a recombinant inbred population from a cross between the maize lines Zong3(with many lateral roots) and 87-1(with few lateral roots).Fine-mapping and functional analysis determined that the candidate gene for qLRT5-1,ZmLRT, expresses the primary transcript for the microRNA miR166a. ZmLRT was highly expressed in root tips and lateral root primordia,and knockout and overexpression of ZmLRT increased and decreased lateral root number,respectively. Compared with 87-1, the ZmLRT gene model of Zong3 lacked the second and third exons and contained a 14 bp deletion at the junction between the first exon and intron,which altered the splicing site. In addition,ZmLRT expression was significantly lower in Zong3 than in 87-1, which might be attributed to the insertions of a transposon and over large DNA fragments in the Zong3 ZmLRT promoter region. These mutations decreased the abundance of mature miR166a in Zong3, resulting in increased lateral roots at the seedling stage.Furthermore, miR166a post-transcriptionally repressed five development-related class-Ⅲ homeodomain-leucine zipper genes. Moreover,knockout of ZmLRT enhanced drought tolerance of maize seedlings. Our study furthers our understanding of the genetic basis of lateral root number variation in maize and highlights ZmLRT as a target for improving drought tolerance in maize.

The TaTCP4/10-B1 cascade regulates awn elongation in wheat(Triticum aestivum L.)

Awns are important morphological markers for wheat and exert a strong physiological effect on wheat yield.The awn elongation suppressor B1 has recently been cloned through association and linkage analysis in wheat.However,the mechanism of awn inhibition centered around B1 remains to be clarified.Here,we identified an allelic variant in the coding region of B1 through analysis of re-sequencing data;this variant causes an amino acid substitution and premature termination,resulting in a long-awn phenotype.Transcriptome analysis indicated that B1 inhibited awn elongation by impeding cytokinin-and auxinpromoted cell division.Moreover,B1 directly repressed the expression of TaRAE2 and TaLks2,whose orthologs have been reported to promote awn development in rice or barley.More importantly,we found that TaTCP4 and TaTCP10 synergistically inhibited the expression of B1,and a G-to-A mutation in the B1 promoter attenuated its inhibition by TaTCP4/10.Taken together,our results reveal novel mechanisms of awn development and provide genetic resources for trait improvement in wheat.