TABLE 1.

A summary of Arabidopsis ER stress response genes and roles as determined by fertility phenotypes in gene knockout mutants.

Gene name	Arabidopsis Gene id	Gene Product Localization	Arabidopsis Mutant	Pollen Development Phenotype at Normal Temperature	Pollen Development Phenotype under Heat Stress	References
bZIP28; BASIC REGION/LEUCINE ZIPPER MOTIF 28	AT3G10800	ER membrane, Cytoplasm, Nucleus	bzip28 bzip60 double mutant	Normal fertility	Reduced fertility, silique lengths in bzip28 bzip60 double mutant plants were largely reduced compared with the wild-type plants	Zhang et al., 2017
bZIP60; BASIC REGION/LEUCINE ZIPPER MOTIF 60	AT1G42990	ER membrane and nucleus
IRE1a; INOSITOL REQUIRING 1A	AT2G17520	ER membrane	ire1a ire1b double mutant	Normal viable pollen	Temperature-sensitive male sterility, improper deposition of pollen coat materials possibly due to tapetal defects, shortened siliques generally devoid of seeds	Deng et al., 2016
IRE1b; INOSITOL REQUIRING 1B	AT5G24360
CNX1; CALNEXIN HOMOLOG 1	AT5G61790	ER membrane	cnx1 crt1 crt2 crt3	Diverse effect on pollen viability and pollen tube growth, leading to a significant reduction pollen mediated transmission		Vu et al., 2017
CRT1; CALRETICULIN1	AT1G56340	ER and vacuole membrane, secretory vesicles
CRT2; CALRETICULIN2	AT1G09210	ER and vacuole membrane, secretory vesicles	cnx1 cnx2 crt1 crt2 crt3	Lethal—no pollen mediated transmission
CRT3; CALRETICULIN3	AT1G08450	ER lumen
BiP1; ER localized member of HSP70 family	AT5G28540	ER lumen and nucleus	bip1 bip2 double mutant	Significant reduction in pollen tube growth activity		Maruyama et al., 2010
BiP2; LUMINAL BINDING PROTEIN	AT5G42020	ER lumen and nucleus	bip1 bip2 bip3 triple mutant	Lethality of pollen due to defects in mitosis1, bicellular stage that contained one or two abnormal microspores with one nucleus		Maruyama et al., 2014
BiP3; HSP70 FAMILY PROTEIN	AT1G09080	ER lumen and nucleus
SHD/HSP90; SHEPHERD, HEAT SHOCK PROTEIN 90-7	AT4G24190	ER lumen	shd	Defects in pollen−tube elongation or penetration into the style	Increased the severity of the defects	Ishiguro et al., 2002
ERdj2A/SEC. 63-1;J-Domain protein	AT1G79940	ER membrane	aterdj2a-1, aterdj2a-2	Defects in pollen germination but not pollen development		Yamamoto et al., 2008
ERdj3A/TMS1; THERMOSENSITIVE MALE STERILE 1	AT3G08970	ER lumen	tms1-1	The fertility of tms1-1 plants was slightly affected, with some ovules in the lower part of the siliques unfertilized	Greatly retarded pollen tube growth in the transmitting tract, resulting in a significant reduction in male fertility	Yang et al., 2009
ERdj3B; J-Domain protein	AT3G62600	ER lumen	erdj3b	Normal flower development and fertility	Produced few seeds at high temperatures due to anther development defects, abnormal enlargement of tapetum cells with vacuolated and aborted microspores, defective pollen release from the anthers	Yamamoto et al., 2020
			atp58ipk aterdj3b	Defects in male gametophyte		Yamamoto et al., 2008
Sec62; protein with similarity to yeast Sec62p.	AT3G20920	ER membrane	atsec62 (T-DNA and amiRNAi)	Smaller and round depressed pollens, defects in pollen development, smaller, aborted, and lesser number of siliques		Hu et al., 2020;
			atsec62	Aborted and mostly empty siliques, delayed anther and pollen development, less pollen released from mutant anthers and reduced pollen germination	Pollen hardly germinated	Mitterreiter et al., 2020
PDI9; PROTEIN DISULFIDE ISOMERASE 9	AT2G32920	ER lumen	pdi9	Normal viable pollen	Disruptions in the reticulated pattern of the exine and an increased adhesion of pollen grains	Feldeverd et al., 2020
PDI10; PROTEIN DISULFIDE ISOMERASE 10	AT1G04980	ER lumen	pdi9 pdi10 double mutant	Normal viable pollen	Completely lost exine reticulation
POD1; POLLEN DEFECTIVE in GUIDANCE 1	AT1G67960	ER lumen	pod1	Pollen tubes fail to target the female gametophyte, defective in micropylar pollen tube guidance leading to zygotic lethality		Li et al., 2011
UTR1, UDP-GALACTOSE TRANSPORTER 1	AT2G02810	ER and golgi membranes	utr1 utr3 double mutant	Abnormalities in both male and female germ line development, haploid atutr1 atutr3 combination is a fully penetrant lethal mutation for the male gametophyte and is partially penetrant for the female gametophyte		Reyes et al., 2010
UTR3, UDP-GALACTOSE TRANSPORTER 3	AT1G14360
STT3a; STAUROSPORIN AND TEMPERATURE SENSITIVE 3-LIKE A	AT5G19690	ER membrane	stt3a-1 stt3b-1 double mutant	Gametophytic lethal		Koiwa et al., 2003
SERK1; SOMATIC EMBRYROGENESIS RECEPTOR-LIKE KINASE 1	AT1G71830	ER and cell membrane	serk1 serk2	Completely male sterile due to a failure in tapetum specification, double mutant anthers lack development of the tapetal cell layer leading to the microspore abortion and male sterility		Albrecht et al., 2005; Colcombet et al., 2005
SAR1; SECRETION ASSOCIATED RAS 1	AT1G56330	ER-, COPII vesicle coat and golgi apparatus	sar1b sar1bsar1c double mutant	Malfunctioning tapetum, leading to male sterility. Microspores in sar1b pollen sacs started to degenerate. The plasma membrane (PM) of microspores in sar1b pollen sacs was detached from the cell wall, and at anther dehiscence, sar1b pollen sacs contained only a pile of cellular debris Microspores aborted at anther developmental stage 10, arrest of pollen development at Pollen Mitosis I		Liang et al., 2020
PDR2, PHOSPHATE DEFICIENCY RESPONSE 2	AT5G23630	ER membrane	mia mutants	Male gametogenesis impaired anthers (mia) show severe reduction in fertility. Mutant microspores fail to separate from tetrads and fragile pollen grains with an abnormal morphology and altered cell wall structure.		Jakobsen et al., 2005
AEP1; ASPARAGINYL ENDOPEPTIDASE 1	AT2G25940	Protein storage vacuole, Vacuole	βvpe	Abnormal degradation of the tapetum, incomplete pollen cytoplasm development, with few oil bodies and an indistinct generative cell. Some of the pollen grains were shrunken and abnormally shaped, immature pollen still contained numerous small vacuoles		Cheng et al., 2020
CEP1; CYSTEINE ENDOPEPTIDASE 1	AT5G50260	ER and vacuole	cep1	Aborted tapetal PCD, reduced male fertility due to impaired pollen development and abnormal pollen exine		Zhang et al., 2014
RBOHE; Riboflavin Synthase-Like Family Protein	AT1G19230	Multi pass membrane protein	rbohe-2	Delayed degeneration of tapetum, reduced pollen viability, abnormal pollen grain shape and exine layer		Xie et al., 2014
RBOHJ; RESPIRATORY BURST OXIDASE HOMOLOG J	AT3G45810	Multi pass membrane protein	rbohH rbohJ double mutant	Pollen tip growth severely impaired due to impaired ROS accumulation		Kaya et al., 2014
RBOHH; RESPIRATORY BURST OXIDASE HOMOLOG J	AT5G60010	Multi pass membrane protein