Mapping and Functional Analysis of a Maize Silkless Mutant sk-A7110

Abstract

The maize (Zea mays) stigma, which is commonly known as silk, is indispensable for reproduction and thus for grain yield. Here, we isolated a spontaneous mutant sk-A7110, which completely lacks silk; scanning electron microscopy showed that the sk-A7110 pistils degenerated during late floret differentiation. Genetic analysis confirmed that this trait was controlled by a recessive nuclear gene and sk-A7110 was mapped to a 74.13-kb region on chromosome 2 between the simple sequence repeat markers LA714 and L277. Sequence analysis of candidate genes in this interval identified a single-nucleotide insertion at position 569 downstream of the transcriptional start site in Zm00001d002970, which encodes a UDP-glycosyltransferase; this insertion produces a frameshift and premature translational termination. RNA-sequencing analysis of young ears identified 258 differentially expressed genes (DEGs) between sk-A7110 and the wild type (WT), including 119 up- and 139 down-regulated genes. Interestingly, most DEGs related to jasmonic acid (JA) synthesis were up-regulated in the mutant compared to WT. Consistent with this, the JA and JA-Isoleucine (JA-Ile) contents were significantly higher in sk-A7110 ears than in WT. At the same time, RNA-sequencing analysis of tassels showed that sk-A7110 could reduce the number of tassel branches in maize by down-regulating the expression of UB2 and UB3 genes. Our identification of the sk-A7110 mutant and the responsible gene will facilitate further studies on female infertility research or maize breeding.

The SAP function in pistil development was proved by two allelic mutations in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

“…These results suggest that CsPID is the gene responsible for the round leaf phenotype. Similar results have been reported in maize [11] and rice [50]. In the present study, the separation ratio of reciprocal crosses between the F 1 ('FT' × fsm1) and F 1 ('FT' × fsm2) plants was 3:1, suggesting that the fsm1 and fsm2 mutants had allelic mutations in the same gene.…”

“…Of these, the “plant hormone signal transduction” pathway (KO04075) was significantly enriched, with 67 DEGs grouped into the auxin (IAA), cytokinin (CK), gibberellin (GA), abscisic acid (ABA), ethylene (ETH), brassinosteroid (BR), jasmonic acid (JA), and salicylic acid (SA) signal transduction pathways. Previous studies have shown that the plant hormones IAA, CK, ETH, GA, JA, and BR can influence the pistil development [ 11 , 47 , 48 ]. Of these, 31 DEGs were enriched in the IAA signal transduction pathway, followed by BR (7 DEGs), JA (5 DEGs), ETH (2 DEGs), CK (1 DEG), and GA (1 DEG) (Additional file 7 : Table S6).…”

“…Hormones play an important role in the regulation of plant growth and development. Multiple mutant genes involved in hormone signaling pathways including the IAA, CK, ETH, GA, JA, and BR pathways have been previously determined in female sterile mutants, resulting in morphological abnormalities in the pistil [ 11 , 34 , 48 , 77 – 80 ]. The transcriptome analysis of female sterile materials showed that DEGs are significantly enriched in the hormone signal transduction pathways in rice, pomegranate, and Pinus tabuliformis , indicating that changes in the hormone metabolic pathway have an important effect on ovule development [ 15 – 17 ].…”

“…3 and Additional file 6: Table S5. Of these, the "plant hormone signal transduction" pathway (KO04075) was [11,47,48]. Of these, 31 DEGs were enriched in the IAA signal transduction pathway, followed by BR (7 DEGs), JA (5 DEGs), ETH (2 DEGs), CK (1 DEG), and GA (1 DEG) (Additional file 7: Table S6).…”

“…Among the floral organs, the pistil has the most complex structure, and its reproductive growth and development processes are regulated by a large number of transcription factors and functional genes [5][6][7]. Several genes regulating pistil development and physiological and biochemical changes during pistil abortion have been identified through mapping and cloning of female sterile mutant genes in Arabidopsis thaliana, rice, cotton, maize, and rapeseed, leading to a gradual understanding of the morphological model and genetic regulation of pistil development [8][9][10][11][12]. Highthroughput transcriptome sequencing of female sterile mutants enables to explore the metabolic pathway changes that occur during pistil abortion at the transcriptional level; screening of key genes regulating pistil development is helpful in studying pistil and ovule development, as well as the genetic regulation mechanism [13][14][15][16][17].…”