Abstract
The husk is a leafy outer tissue that encloses a maize ear. Previously, we identified the optimum husk structure by measuring the husk length, husk layer number, husk thickness and husk width. Husk tightness (HTI) is a combined trait based on the above four husk measurements. Unveiling the genetic basis of HTI will aid in guiding the genetic improvement of maize for mechanical harvesting and for protecting the ear from pest damage and pathogen infection. Here, we used a maize associate population of 508 inbred lines with tropical, subtropical and temperate backgrounds to analyze the genetic architecture of HTI. Evaluating the phenotypic diversity in three different environments showed that HTI exhibited broad natural variations and a moderate heritability level of 0.41. A diversity analysis indicated that the inbred lines having a temperate background were more loosely related than those having a tropical or subtropical background. HTI showed significant negative correlations with husk thickness and width, which indicates that thicker and wider husks wrapped the ear tighter than thinner and slimmer husks. Combining husk traits with ∼1.25 million single nucleotide polymorphisms in a genome-wide association study revealed 27 variants that were significantly associated with HTI above the threshold of P < 7.26 × 10–6. We found 27 candidate genes for HTI that may participate in (1) husk senescence involving lipid peroxidation (GRMZM2G017616) and programmed cell death (GRMZM2G168898 and GRMZM2G035045); (2) husk morphogenesis involving cell division (GRMZM5G869246) and cell wall architecture (GRMZM2G319798); and (3) cell signal transduction involving protein phosphorylation (GRMZM2G149277 and GRMZM2G004207) and the ABSISIC ACID INSENSITIVE3/VIVIPAROUS1 transcription factor (GRMZM2G088427). These results provide useful information for understanding the genetic basis of husk development. Further studies of identified candidate genes will help elucidate the molecular pathways that regulate HTI in maize.
Highlights
Maize is the number one production crop in China and in the world, it plays a vital role in ensuring global food security (Lawrence et al, 2008; Shaokun et al, 2017)
The result showed that the panel was divided in to four subgroups, which was consistent with the previous study (Yang et al, 2011)
It can be explained by the fact that tropical maize lines have undergone more intense recombination and contain more rare alleles than temperate maize lines (Lu et al, 2011), since the stiff stalk (SS) and non-stiff stalk (NSS) subgroups belonged to the temperate kinship and the TST subgroup belonged to the tropical and subtropical kinship
Summary
Maize is the number one production crop in China and in the world, it plays a vital role in ensuring global food security (Lawrence et al, 2008; Shaokun et al, 2017). Husk tightness (HTI) is an important husk trait that plays an important role in ear growth. HTI is negatively correlated with the water content of the ear after physiological maturity (Li et al, 2014). Loose husks result in faster cob and ear drying rates compared with normal or tight husk (Hicks et al, 1976). Breeding varieties with rapid physiological maturation rates and low water contents, which are suitable for mechanized harvesting, is a serious goal. The husk protects the ear from pest damage and pathogen infection (Barry et al, 1986; Warfield and Davis, 1996). Dissecting the genetic basis of HTI would aid the genetic improvement of maize for mechanical harvesting and for protecting the ear from pest damage and pathogen infection
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