Fertility of Pedicellate Spikelets in Sorghum Is Controlled by a Jasmonic Acid Regulatory Module.

Nicholas Gladman,Lifang Zhang,Chad Hayes,John Burke,Michael Regulski,Doreen Ware,Ratan Chopra,Shawn A Christensen,Zhanguo Xin,Gloria Burow,Yinping Jiao,Junping Chen,Lavanya Dampanaboina,Young Koung Lee

doi:10.3390/ijms20194951

Abstract

As in other cereal crops, the panicles of sorghum (Sorghum bicolor (L.) Moench) comprise two types of floral spikelets (grass flowers). Only sessile spikelets (SSs) are capable of producing viable grains, whereas pedicellate spikelets (PSs) cease development after initiation and eventually abort. Consequently, grain number per panicle (GNP) is lower than the total number of flowers produced per panicle. The mechanism underlying this differential fertility is not well understood. To investigate this issue, we isolated a series of ethyl methane sulfonate (EMS)-induced multiseeded (msd) mutants that result in full spikelet fertility, effectively doubling GNP. Previously, we showed that MSD1 is a TCP (Teosinte branched/Cycloidea/PCF) transcription factor that regulates jasmonic acid (JA) biosynthesis, and ultimately floral sex organ development. Here, we show that MSD2 encodes a lipoxygenase (LOX) that catalyzes the first committed step of JA biosynthesis. Further, we demonstrate that MSD1 binds to the promoters of MSD2 and other JA pathway genes. Together, these results show that a JA-induced module regulates sorghum panicle development and spikelet fertility. The findings advance our understanding of inflorescence development and could lead to new strategies for increasing GNP and grain yield in sorghum and other cereal crops.

Highlights

Sorghum (Sorghum bicolor (L.) Moench) is a crop plant domesticated in northern Africa ~6000 years ago [1,2]
Sorghum bicolor (L.) Moench plants manifesting the multiseeded phenotype were identified from a collection of ethyl methane sulfonate (EMS)-induced single nucleotide polymorphisms (SNP) [24]
MSD1 has the capacity to bind the promoter of MSD2, as well as promoters and more distant genetic elements associated with developmental and jasmonic acid (JA) pathway genes, including those encoding other LOX-domain containing proteins

Summary

Introduction

Sorghum (Sorghum bicolor (L.) Moench) is a crop plant domesticated in northern Africa ~6000 years ago [1,2]. A C4 grass with robust tolerance to drought, heat, and high-salt conditions, sorghum is the fifth most agriculturally important crop in terms of global dedicated acreage and production quantity. It serves as a useful model for crop research due to its completely sequenced compact genome (~730 Mb) [3] and similarity to the functional genomics capabilities of maize, sugarcane, and other bioenergy grasses comprising more convoluted genomes. A terminal trio of spikelet florets are attached through a pedicel to these branches: one sessile spikelet (SS) that is fertile and two pedicellate spikelets (PSs) that fail to generate mature pistils and sometimes anthers, which results in an inability of PSs to fertilize They will senesce during grain filling instead of becoming viable seed [6]. This terminal spikelet group, several pairs of SSs and PSs populate the branches down to the nodes

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Conclusion