Abstract
Flower opening is a process that requires movement of petals from a closed position to a horizontal open position, while petal abscission requires cell-wall disassembly. Both processes are controlled by ethylene and require cell-wall modification at the junction (abscission zone) of the petal and thalamus to facilitate the movement or separ- ationofpetals.Inthepresentstudy,afamilyofxyloglucanendotransglucosylase/hydrolase(XTH)geneswasstudiedto understand their role in petal abscission in flowers of Rosa bourboniana (ethylene sensitive, early abscising) and Rosa hybrida(lessethylenesensitive,lateabscising).TranscriptomesequencingofpetalabscissionzonecDNAwasperformed atdifferenttimepoints(ethylenetreatedanduntreated)andscreenedforXTHgenes.ThestudyidentifiedninenewXTH genes that showed differential changes in gene expression during flower opening and abscission. Of these, RbXTH3, RbXTH5, RbXTH6 and RbXTH12 were rapidly induced by ethylene within 1-4 h of ethylene treatment, corresponding to the period of flower opening. These genes also showed an early up-regulation during flower opening under ethylene-untreated (field abscission) conditions, indicating a possible role in anthesis and petal movement during flower opening. Other genes such as RbXTH4 and RbXTH9 were up-regulated later at 8-12 h after ethylene treatment and at 24-36 h under natural abscission conditions, indicating a possible role in abscission. Treatment with a higher ethylenedose(15 m LL 21 ethylene)acceleratedabscission,leadingtohighersteady-statelevelsofXTHgenetranscripts atanearliertimepointcomparedwith0.5 m LL 21 ethylene.Incontrast,transcriptaccumulationofmostoftheXTHswas considerablydelayedin thelate-abscising rose,R.hybrida, inkeeping with the slowerfloweropeningand delayedpetal abscission. The results suggest coordinated action of different XTHs in cell-wall modification of xyloglucan moieties during flower opening as well as cell separation during abscission.
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