Abstract
Metaxylem vessels in maize brace roots are key tissue, and their number (MVN) affects plant water and inorganic salt transportation and lodging resistance. Dissecting the genetic basis of MVN in maize brace roots can help guide the genetic improvement of maize drought resistance and lodging resistance during late developmental stages. In this study, we used 508 inbred lines with tropical, subtropical, and temperate backgrounds to analyze the genetic architecture of MVN in maize brace roots. The phenotypic variation in MVN in brace roots was evaluated in three environments, which revealed broad natural variation and relative low levels of heritability (h2 = 0.42). Stiff-stalk lines with a temperate background tended to have higher MVNs than plants in other genetic backgrounds. MVN was significantly positively correlated with plant height, tassel maximum axis length, ear length, and kernel number per row, which indicates that MVN may affect plant morphological development and yield. In addition, MVN was extremely significantly negatively correlated with brace root radius, but significantly positively correlated with brace root angle (BRA), diameter, and number, thus suggesting that the morphological function of some brace root traits may be essentially determined by MVN. Association analysis of MVN in brace roots combined 1,253,814 single nucleotide polymorphisms (SNPs) using FarmCPU revealed a total of nine SNPs significantly associated with MVN at P < 7.96 × 10–7. Five candidate genes for MVN that may participate in secondary wall formation (GRMZM2G168365, GRMZM2G470499, and GRMZM2G028982) and regulate flowering time (GRMZM2G381691 and GRMZM2G449165). These results provide useful information for understanding the genetic basis of MVN in brace root development. Further functional studies of identified candidate genes should help elucidate the molecular pathways that regulate MVN in maize brace roots.
Highlights
Water is an important environmental factor with a profound effect on plant growth and development
The formation of metaxylem vessels is accompanied by the thickening of secondary cell walls (Turner et al, 2007; Furuta et al, 2014), which are composed of cellulose, hemicellulose and lignin, metaxylem vessel number (MVN) can affect the mechanical strength of brace roots and their structural supporting capacity in maize (Zhao and Dixon, 2011; Oda and Fukuda, 2012; Voxeur et al, 2015; Zhao, 2016)
We have revealed the genetic architecture of natural variation in MVN in maize brace roots by the Genome-wide association study (GWAS) approach
Summary
Water is an important environmental factor with a profound effect on plant growth and development. As a vascular plant species, maize has evolved a xylem vessel system that transports materials such as water and inorganic salts to support plant growth and development. Maize brace roots, which are specialized structures, have developed metaxylem vessels. As an important part of postembryonic roots, brace roots provide water and inorganic substances for maize plants during later stages of growth and development, when seminal roots and primary roots have degraded (Hoppe et al, 1986; Wang and Bai, 2019). The formation of metaxylem vessels is accompanied by the thickening of secondary cell walls (Turner et al, 2007; Furuta et al, 2014), which are composed of cellulose, hemicellulose and lignin, MVN can affect the mechanical strength of brace roots and their structural supporting capacity in maize (Zhao and Dixon, 2011; Oda and Fukuda, 2012; Voxeur et al, 2015; Zhao, 2016). Dissecting the genetic basis of the MVN in brace roots should contribute to the genetic improvement of drought resistance and lodging resistance during late stages of maize development
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