Characterization of Ppd-D1 alleles on the developmental traits and rhythmic expression of

Characterization of Ppd-D1 alleles on the developmental traits and rhythmic expression of

photoperiod genes in common wheat

ZHAO Yong-ying1,2*,WANG Xiang1*,WEI Li1,WANG Jing-xuan1,YIN Jun1 1National Engineering Research Center for Wheat/Collaborative Innovation Center of Henan Grain Crops/State Key Laboratory of Wheat and Maize Crop Science/College of Agriculture,Henan Agricultural University,Zhengzhou 450002,P.R.China2National Laboratory of Wheat Engineering/Key Laboratory of Wheat Biology and Genetic Breeding in Central Huang-Huai Region,Ministry of Agricultural/Key Laboratory of Wheat Biology of Henan Province/Wheat Research Institution,Henan Academy of Agricultural Sciences,Zhengzhou 450002,P.R.China ¡¾ÆÚ¿¯Ãû³Æ¡¿Å©Òµ¿Æѧѧ±¨£¨Ó¢Îİ棩 ¡¾Äê(¾í),ÆÚ¡¿2016(015)003 ¡¾×ÜÒ³Êý¡¿10 ¡¾

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Keywords:

wheat

photoperiod,spike

differentiation,heading,gene expression,Ppd-D1 Abstract

Photoperiodic response is an important characteristic that plays an important role in plant adaptability for various environments.Wheat cultivars grow widely and have high yield potential for the strong photoperiod adaptibility.To assess the photoperiodic response of

different genotypes in wheat cultivars,the photoperiodic effects of the Ppd-D1 alleles and the expressions of the related TaGI,TaCO and TaFT genes in Liaochun 10 and Ningchun 36 were investigated under the short-day£¨6 h light,SD£©,moderate-day£¨12 h light,MD£©and long-day£¨24 h light,LD£©conditions.Amplicon length comparison indicated that the promoter of Ppd-D1 in Ningchun 36 is intact,while Liaochun 10 presented the partial sequence deletion of Ppd-D1 promoter.The durations of all developmental stages of the two cultivars were reduced by subjection to an extended photoperiod,except for the stamen and pistil differentiation stage in the Liaochun 10 cultivar.The expression levels of the Ppd-D1 alleles and the TaGI,TaCO and TaFT genes associated with the photoperiod pathway were examined over a 24-h period under SD and MD conditions.The relationships of different photoperiodic responses of the two cultivars and the expression of photoperiod

pathway

genes

were

analyzed

accordingly.The

photoperiod insensitive£¨PI£©genotype plants flower early under SD; meanwhile,the abnormal expression of the Ppd-D1a allele is accompanied with an increase in TaFT1 expression and the TaCO expression variation.The results would facilitate molecular breeding in wheat.

Received 11 February,2015 Accepted 1 July,2015

ZHAO Yong-ying,Mobile: +86-13513895016,Tel: +86-371-65750512,E-

mail: yongying001@126.com; Correspondence YIN Jun,Tel/Fax: +86-371-63558203,E-mail: xmzxyj@126.com

*These authors contributed equally to this study.

? 2016,CAAS.All rights reserved.Published by Elsevier Ltd.

1.Introduction

Wheat£¨Triticum aestivum£©is one of the world¡¯s most important food crops,and is widely cultivated because of its adaptation to various environments.Photoperiodic response is considered an important physiological characteristic in wheat,because the yield significantly increases if the circadian rhythm corresponds to the day/night cycle of the region in which wheat is grown.

Photoperiodic response coordinates with the vernaliza-tion of wheat,in order to carry out the heading and flowering processes,because in order to flower,wheat seedlings must first experience a period of cold,as well as a particular photoperiod£¨Gonzalez et al.2002; Kumar et al.2012; Jokela et al.2014£©.Wheat cultivars can be classified according to photoperiod susceptibility,into photoperiod sensitive£¨PS£©or photoperiod insensitive£¨PI£©types.In PS wheat cultivars,flowering occurs earlier under long-day condition£¨LD£©and is delayed under short-day condition£¨SD£©.PS cultivars are often distributed at high latitudes,while PI cultivars predominate in low-latitude regions with SD,such as southern Europe£¨Worland 1996; Foulkes et al.2004; Lobell

and Field 2007£©.In China,most improved cultivars are of the PI types; PS types can only be found in spring wheat regions at high latitudes,such as northwestern China,and in the winter wheat regions of the Gansu and Xinjiang,China£¨Yang et al.2009; Guo et al.2010£©.

In hexaploid wheat,the photoperiodic response is primarily controlled by three major genes,Ppd-D1£¨Photoperiod-D1,previously known Ppd1£©,Ppd-B1£¨Ppd2£©and Ppd-A1£¨Ppd3£©,which are located on the short arms of the group 2 chromosomes£¨Welsh et al.1973; Scarth and Law 1983,1984; Beales et al.2007£©.In PI phenotypes,Ppd alleles are given a suffix and designated as Ppd-D1a,Ppd-B1a or Ppd-A1a£¨McIntosh et al.2003£©.Ppd-D1 is located on chromosome 2D,and has a stronger effect on heading time than other Ppd-1 alleles£¨Law et al.1978£©.Homolog comparisons revealed that Ppd-1 is a homolog of the Ppd-H1 gene in barley,and that the barley homolog Ppd-H1 is a member of the pseudo-response regulator£¨PRR£©gene family£¨Turner et al.2005; Beales et al.2007£©.Ppd-D1a in PI wheat is associated with a 2 089-bp deletion upstream of the coding region£¨Beales et al.2007£©.For the Ppd-A1a alleles in PI genotype,a 1 027-,1 117- or 1 085-bp deletions in the upstream of the coding region have been observed,while Ppd-B1a is associated with a 308-bp insertion upstream of the coding region£¨Wilhelm et al.2009; Nishida et al.2013£©.Among different

Ppd-1b

genotypes,studies

using

near-isogenic

and

chromosome introgression lines indicated that flowering is triggered by long photoperiods and inhibited by short photoperiods£¨Whitechurch and Slafer 2001,2002; Gonzalez et al.2002,2005; Dyck et al.2004; Bentley et al.2011; Seki et al.2011£©.Of the three mutant Ppd alleles,Ppd-D1a confers the earliest flowering time,followed by Ppd-A1a and Ppd-B1a£¨Scarth and Law 1984; Bentley et al.2011£©.

The alteration of PRR genes could influence the expression profiles of photoperiod pathway genes£¨Turner et al.2005; Locke et al.2006; Pokhilko et al.2012£©.In wheat,the Ppd-1a allele was found to be misexpressed in PI genotypes,with its peak expression time shifted from light to dark period£¨Beales et al.2007£©.In addition,the expression of TaGI£¨GIGANTEA£©was unaltered,but that of TaCO1£¨CONSTANS 1£©was significantly reduced.There was a clear effect on TaFT1£¨FLOWERING LOCUS T 1£©expression,which increases in the photoperiod

insensitive£¨Ppd-D1a£©genotype£¨Beales

et

al.2007£©.According to the 2A PRR transcript analysis,the PS lines revealed a peak in expression at 6 h,and a subsequent drop to very low expression levels during the dark period.Meanwhile,the PI lines did not exhibit this pattern,expressing the gene at high levels throughout the day£¨Wilhelm et al.2009£©.However,Guo et al.£¨2010£©found that the expression of Ppd genes varied among haplotypes,even though the expression peaks occurred at the same time£¨Guo et al.2010£©.