Hull-splitting is caused by a mutation of the gene Os04g0447100 in rice

Rice hull, consisted of lemma and palea, is an important organ that helps protect seeds, determines seed shape, and ensures grain filling. We identified the split-hull (sph) mutant in rice through chemical mutagenesis, which exhibits hull-splitting in the interlocking part between lemma and palea and/or the folded part of the lemma during the grain filling stage. Morphological and chemical analysis revealed that reduction in the width of the lemma and lignin content of the hull in the sph mutant might be the cause of hull-splitting. Genetic analysis indicated that the mutant phenotype was controlled by a recessive gene, sph (Os04g0447100), which encodes a type-2 13-lipoxygenase. SPH knockout- and knockdown-transgenic plants displayed the same as in the mutant. The sph mutant showed significantly higher linoleic and linolenic acid (substrates of lipoxygenase) contents in spikelets compared to the wild type probably due to the genetic defect of SPH and subsequent decrease in lipoxygenase activity. In dehulling experiment, the sph mutant showed high dehulling efficiency even by a weak tearing force in a dehulling machine. The results provide a basis for understanding of the functional role of lipoxygenase in structure and maintenance of hulls, and might facilitate breeding of easy-dehulling rice. This study was supported by a grant from the Next-Generation BioGreen21 Program (No. PJ013165) of the Rural Development Administration, Korea.
Take Away Notes:
• A new type spikelet mutant in rice.
• Map-based cloning of mutant traits.
• How to confirm the genes through transgenic and PCR technology.