Genome-Wide and GWAS Dissection of Maize Fibrillin Genes Reveals Plastid Regulators of Drought and Salt Stress Tolerance

Fibrillins (FBNs) are conserved plastid-associated proteins implicated in plant development and abiotic stress responses; however, their roles in maize remain unclear. In this study, through a genome-wide bioinformatic analysis, we identified 14 ZmFBN genes in the maize genome and characterized their phylogeny, chromosomal distribution, gene structure, conserved motifs, and promoter cis-elements. ZmFBN members were grouped into several subfamilies that all retain a conserved PAP_fibrillin domain, whereas the variation in exon-intron organization, motif composition, and regulatory elements suggests functional diversification. Expression profiling revealed pronounced tissue-preferential patterns, with many genes highly expressed in leaves and reproductive tissues, and distinct responses to drought, salt, heat, and cold stresses. qRT-PCR assays showed that ZmFBN8 and ZmFBN9 are strongly induced by both salt and PEG-simulated drought, ZmFBN2 and ZmFBN5 are predominantly drought-responsive, and ZmFBN11 is mainly activated by salt. Genome-wide association analysis further detected significant loci near ZmFBN1 and ZmFBN4, whose allelic variants are associated with the survival rate under drought and with key agronomic traits, including the tassel branch number, flowering time, ear diameter, and kernel length. These results demonstrate that ZmFBN genes make diversified contributions to maize growth, development, and stress adaptation and highlight several members as promising targets for functional studies and the molecular breeding of stress-tolerant maize. Moreover, selection pressure analysis indicated ZmFBN7 experienced relaxed purifying selection, and ZmFBN12 underwent positive selection, which drives the functional diversification of the ZmFBN family during maize evolution.