Study On Internode Elongation In Poaceae

Poaceae is an important large family in plant kingdom,and major stable food crops like rice,wheat,maize,sorghum,millet and barley belong to this group.Semi-dwarfism breeding in wheat and rice significantly increased yield and facilitate "green revolution",thus plant height is an important agricultural trait in crop breeding.The stem thickness in poaceae determines the lodging resistance and consequentially plays an important role in yield.The plant height of poaceae is determined by both the number of internodes and their lengths,the strength of stem is determined by the diameter and the thickness of internode.Thus,it is of great importance to study the internode elongation and thickening in poaceae for both theory and breeding.Number and elongation of their internodes in 24 species poaceae plants from 7 subfamilies were statistically analyzed.We also investigated the diameter and thickness of each internode in rice.Longitudinal and vertical cell layer and cell length were analyzed in rice,green bristlegrass and millet.Based on a short tandem target mimic microRNA172(miR172STTM)material,we explored the possible mechanism of microRNA172 affects the internode elongation in poaceae.The main results were as follows:(a)Based on systemic investigation of internode length in poaceae,we divided this family into three groups,the snail type,the peak type and the harp type.The snail type was characterized by the longest uppermost internode,the second longest middle internodes and shorter basal and upper internodes;the peak type was characterized longest middle internodes and shorter basal and upper internodes;while the harp type was characterized by gradually longer from the basal internode to upper ones.Among the investigated 24 species,which belongs to 23 genus,16 belongs to the harp type,accounting for 66.6%in the total investigated species.While both the snail type and the peak type account for 16.7%.(b)Variations of the internode length in wild species were relatively greater than that in the domesticated crops,suggesting that the domestication might play a role in internode elongation.The internode elongation of millet belonged to the harp pattern,while its wild species green bristlegrass is belonged to the peak type,suggesting that domestication could change the internode elongation pattern..(c)We analyzed longitudinal cell length of each internode at 20%,40%,60%and 80%location of multiple internodes in two harp type internode elongation pattern species(rice and green bristlegrass)and one snail type plant(millet).In rice the longitudinal cell length at the same location exhibited extended and then shortened tendency from down up.It became gradually shorter from down up in the same internode.In green bristlegrass,the longitudinal cell length in the different internode from down up display no change in 20%position,gradually shorter in 40%position,shorter then longer and shorter again in both 60%and 80%positions.In the first,second and third internodes of green bristlegrass,longitudinal cell length displayed shorter and then longer from down up,while it become longer and then shorter in the fourth internode.In millet,the longitudinal cell lengths of different internodes increased firstly,then decreased and then increased again from down up at 20%position,which is consistent with the internode elongation pattern.The longitudinal cell length at 40%position increased gradually from down up,while increased firstly and then decreased at 60%position.Cell length in the first internode decreased firstly and then increased from down up,while,it exhibited a contradictory tendency in the second internode.Taken together,there was no significant positive correlation between cell elongation and internode elongation in most of the cases,suggesting that cell number determines the internode elongation pattern.(d)The stem diameter and stem thickness at 40%position of each internode decreased from down up in rice,this physical structure might facilitate to support the above ground tissues and increase lodging resistance.Cell layer number at 40%position of each internode in the vertical section was decreased gradually from down up in rice,green bristlegrass and millet.In rice and green birstlegrass,cell width at 40%position of each internode was decreased slightly from down up,while in millet,cell width displayed no significant change,suggesting cell layer number increase or cell proliferation is the dominant factor that affects internode thickness.(e)Rice showed reduced plant height,decreased internode length and embedded panicle phenotype when knocking down microRNA172 using a short tandem target mimic technology(STTM).Compared with wild type,each internode become shorter in miR172STTM lines,especially in the uppermost internode.However,cell length was not significantly decreased in microRNA 172STTM rice plants,suggesting that microRNA172 might regulate internode elongation through cell proliferation.This study focused on internode elongation mechanisms of poaceae species.Based on the internode elongation patterns,we divided the poaceae into three groups.The molecular mechanism underlying longitudinal and vertical growth of internode was revealed.