Ethylene Responses in Rice Roots and Coleoptiles Are Differentially Regulated by a Carotenoid Isomerase-Mediated Abscisic Acid Pathway
Cui-Cui Yin,Biao Ma,Derek Phillip Collinge,Barry James Pogson,Si-Jie He,QingXiong,Kai-Xuan Duan,Hui Chen,Chao Yang,Xiang Lu,Yi-Qin Wang,Wan-KeZhang,Cheng-Cai Chu,Xiao-Hong Sun,Shuang Fang,Jin-Fang Chu,Tie-GangLu,Shou-Yi Chen,and Jin-Song Zhang

The Plant Cell

http://www.plantcell.org/content/early/2015/03/31/tpc.15.00080

Abstract
Ethylene and abscisic acid (ABA) act synergistically or antagonistically toregulate plant growth and development. ABA is derived from thecarotenoid biosynthesis pathway. Here, we analyzed the interplay amongethylene, carotenoid biogenesis, and ABA in rice (Oryza sativa) usingthe rice ethylene response mutant mhz5, which displays a reducedethylene response in roots but an enhanced ethylene response incoleoptiles. We found that MHZ5 encodes a carotenoid isomerase and thatthe mutation in mhz5 blocks carotenoid biosynthesis, reducesABAaccumulation, and promotes ethylene production in etiolatedseedlings. ABA can largely rescue the ethylene response of the mhz5mutant. Ethylene induces MHZ5expression, the production of neoxanthin,an ABA biosynthesis precursor, andABA accumulation in roots. MHZ5overexpression results in enhanced ethylene sensitivity in roots andreduced ethylene sensitivity in coleoptiles. Mutation or overexpressionof MHZ5 also alters the expression of ethylene-responsive genes. Genetic studies revealed that the MHZ5-mediated ABA pathway acts downstream ofethylene signaling to inhibit root growth. The MHZ5-mediated ABA pathway likely acts upstream but negatively regulates ethylene signaling tocontrol coleoptile growth. Our study reveals novel interactions amongethylene, carotenogenesis, and ABA and provides insight intoimprovements in agronomic traits and adaptive growth through themanipulation of these pathways in rice.